If you feel confused about your gender, you're not alone. Like adults, teenagers can experience a range of feelings about being male or female.
Most young people grow up thinking of themselves as either a boy or a girl and don't question which they are (their gender). But for some people, gender is more complicated.
According to Ady Davis, who works as a psychosexual therapist with the North-East Gender Dysphoria Service, people can experience a range of feelings about their gender.
"Sometimes your feelings about your gender aren't clear and you can't identify with either sex. Sometimes people question their gender if their interests and socialising don't fit with their birth gender. For example, if you're a boy who prefers the company of girls.
"Some people feel that they're both male and female. Others have a strong sense of being the opposite gender. Perhaps they've felt trapped in the wrong body since early childhood.
"For young people who feel uncomfortable about their gender, puberty can be a very difficult time," says Davis. "Your biological gender is physically marked by body changes, such as the growth of breasts or facial hair."
Does it make me gay, lesbian or bisexual?
Gender identity (how you feel about your gender) and sexuality (your sexual preferences) aren't the same thing, but they're both linked.
"Sometimes a young person comes out as lesbian or gay, but when they start forming relationships they don't feel like it's a same-sex relationship," says Davis.
"Equally, there are other people who can't figure out who they're attracted to because they're uncomfortable with their own gender identity.
"There are also people who know who they're attracted to, but they hate their body so much that they avoid relationships because they can't stand the thought of being touched."
According to Davis, some teenagers gravitate towards a scene or a community that gives them a chance to explore their sexuality and gender identity in a safe way. "For example, in the goth scene gender and sexuality aren't so clearly defined."
How can it affect you?
Teenagers who experience gender discomfort might feel unhappy, lonely or isolated from other teenagers.
They may feel social pressure from classmates, teachers and family to conform to gender stereotypes, or they may face bullying and harassment. Their discomfort about being male or female may affect their self-esteem and their performance at school.
All these difficulties can affect the person's health. "Some teenagers self-harm or face suicidal feelings. Depression is very, very common among young people with gender discomfort," says Davis.
If you're experiencing any of these feelings, get medical help.
Who can I turn to for help?
If you're experiencing discomfort or uncertainty about your gender, the important thing is to talk to an adult you trust. Don't suffer in silence.
Your parents may be much more supportive than you expect. Schools and colleges sometimes have counsellors that young people can speak to in confidence.
If you don't feel able to talk to someone you know, there are several charities that provide support to young people.
Mermaids is a support group specifically for children and young people who are trying to cope with gender identity issues. You can call the Mermaids telephone helpline on 020 8123 4819 (open Monday to Saturday, 3-7pm) for advice, information and help.
There are also real stories on the Mermaids website about issues such as coming out.
ChildLine, the children and young people's helpline, is there for anyone who wants to talk about a problem in confidence. Call 0800 1111, or visit the ChildLine website.
Gendered Intelligence runs projects that enable young trans people to meet. Find out more on the Gendered Intelligence website.
The first step is for you to see your GP. They will usually refer you to a team that's skilled in supporting young people, known as Child and Adolescent Mental Health Service teams (CAMHS).
You can discuss your gender issues with someone from these teams in a non-judgemental environment.
The people who support you may also offer support to your parents and family, and may also get in touch with your school.
Coming out as trans
Deciding who to tell about how you feel, and when, is a personal decision. Coming out, or revealing to others that you're trans, can be difficult because of other people's reactions.
But if a young person is supported by family and friends and is given an opportunity to talk about their feelings at school, coming out can be very positive.
For more information, see Coming out as trans.
A very high proportion of trans adults say they were bullied at school. Some people experience transphobic bullying – they're bullied specifically for being trans. Others are bullied simply for being different.
Bullying of any type is unacceptable, and you don't have to put up with it. For more on how to deal with bullying, see Bullying: where to find help.
What medical help is available?
If you have strong and persistent feelings of being the opposite gender and decide you want to live full-time as the opposite gender (called transitioning), there are various medical options in the long term. These include counselling, hormonal treatment and surgery.
If you are under 16, you may be offered psychological therapy to help you cope with the discomfort you feel about your gender identity.
This may be offered through your local Child and Adolescent Mental Health Service (CAMHS), or you may be referred to the only specialist clinic for young people with gender identity issues at the Tavistock and Portman in London.
Some young people who are referred to the Tavistock and Portman may be offered hormone blockers in addition to psychological therapy. Hormone blockers delay the physical changes of puberty. This gives the young person time to decide whether to live as a man or woman in the long term.
The age at which hormonal treatment may be offered has been lowered from 16 to 12 since January 2011 under a research study being carried out by the Tavistock and Portman into the effects of hormone blockers earlier in puberty.
From the age of 16, if you require further treatment, you may be offered cross-sex hormonal medication (hormones to make you more masculine or more feminine) after an assessment.
The decision to start cross-sex hormonal medication requires very careful consideration because some of the physical changes caused by these hormones can't be reversed, such as a lower voice and facial hair from male hormones.
Currently, the only centre that can prescribe hormonal treatment on the NHS to young people aged under 18 is the gender identity service at the Tavistock and Portman in London. From the age of 18, young people are eligible for treatment in adult NHS gender clinics.