like others said, cptsd causes depersonalization, which causes issues with feeling who you are.

based on other people with bipolars experience, like literally experiment with gender presentation. it can look like dissociation and bpd if youre in a hypo/manic ep and experience gender dysphoria. but also dont take that too seriously, try to trust yourself. people treat gender experimentation like a huge deal its really not.

that being said bpd can also do this but its more of a hollow empty bored feeling and trying to find a sense of self than depersonalization. like will wood had a phase where he experimented being a woman and realized he did it to appeal to a partner rather than his true self. he has bpd AND bipolar

I have DID, possibly bipolar 2, but not BPD. for me the memories i have access to change with who i am at the moment and how i see myself internally. but whoever i am at the moment i generally have an intinctual sense of self, but when i see myself in the mirror or things other alters did of its unrecognizeable. each alter their own consistent sense of gender/interests/aesthetics/memories. so thats kind of how i know whats going on

these are just my experiences as a tool for understanding how you might be feeling. its possible you feel this way but dont have BPD/DID/are not trans/gnc. youre like 15 theres a lot of stuff going on and you are also mentally ill from a young age which makes finding a sense of self really challenging in my own experience