I'm a girl but I feel like a boy sometimes. But it changes so quickly that I'm not sure what I am. How do I identify myself?

I've gone through an experience like this myself. It can be a very difficult time. It seems like you may be questioning your gender identity. In regards to gender identity, there are three most common gender identities. Transgender Female to Male, Transgender Male to Female, and Genderfluid. Genderfluid seems to fit most with what you've asked about. Genderfluid is classified as a gender expression in which an individual sometimes identifies and/or expresses themselves as a female at some times and a male at others. Genderfluidity can come in all shapes and sizes. Coming and going. The time frame at which you may identify with each gender varies between person to person. Many people who identify as genderfluid end up changing their names and/or pronouns to fit their identity. Common pronouns among genderfluid individuals are they/them.

I felt a similar way; I identify as non-binary. It’s been liberating to finally be able to “fit” somewhere. I am AFAB (assigned female at birth) but never quite tidily fit into that gender or category. It’s been a long and fruitful journey and I have been very grateful to have met wonderful and supportive individuals along the way. I hope you are able to have a similar experience while discovering your own unique identity! If this sounds like something you’d like to discuss further please don’t hesitate to reach out. Wishing you all the best. - B

What you describe would usually be called non-binary or genderqueer. Your gender identity can change of course - you may end up feeling like a boy all the time, or a girl all the time, or non-binary. You should identify yourself however it feels comfortable to you. This can be different with different groups of people, and with yourself. I happen to be a transsexual man, and even though I felt like a boy all the time, and then a man all the time, it took years for me to figure out and understand my feelings, and who I was. I'm not genderqueer or non-binary, but I have friends who identify that way. I hope that helps.

If your gender identification is variable and it can change from time to time, this would match the definition of genderfluid, a type of non-binary gender identity.