I'm 15 and I remember nothing from my childhood how come I don't remember anything

Really depends on how far back you are trying to think of.
Also pictures, sights, sounds and smells will trigger memories.

Maybe you just don't want to remember but you think you do ,maybe something happened and your family does not want you to know you have to think of the what ifs not the whys / how comes

My bad I meant some times you have to think of the what is cause the whys and how comes will get you nowhere