You are not alone. Most people identify strongly with the gender they’re expected to grow up as. But it’s not uncommon for a person to identify strongly with the other gender. Sometimes the desire lasts only a brief time. Sometimes it lasts a lifetime.
The desire to be another gender occurs when one’s sexual anatomy is in conflict with one’s gender identity. It may be about an erotic desire to be in the role of the other gender, to play the roles and have the privileges of the other gender, or it may be related to a feeling that one was born into the “wrong” body. Or it could be all three.
People who want to live the role of the opposite gender are called transgender. Transgender people feel that the body type and sex organs they were born with (a penis or vulva) are different from the gender they want to be (being a guy or a girl).
Some transgender people choose to live the role of the gender they identify with, and some don’t. Some transgender people choose to become transsexual by having their gender reassigned through hormone treatments and/or surgery.
Many people, including teens, have non-traditional feelings about gender roles and sexual identities, and that is normal, too.
It’s important to talk to someone you can trust, and who understands gender identity issues. To find a support group in your area, check out PFLAG's chapter locator and CenterLink's LGBTQ+ center locator. They have a database of thousands of support groups and other resources for lesbian, gay, bisexual, transgender, and queer or questioning youth.