Memory problems - severe. Help please?

Okay, I'm a 17 y/o male and I cannot remember anything from my childhood. Literally nothing until age 12 roughly. I've unconciously tried to fill the void by fabricating memories, but recently found out that they were false. Why could this be? Obviously I don't know why or when I forgot everything...It's so frustrating. My mom said I didnt have any trauma or an accident that could cause amnesia, and I think it may have been a gradual thing...help??