You do not qualify for Social Seciurity/SSDI, that's a long-time work history thing. SSI is "supplemental" income to help augment what you are living on if it is decided disability is what is keeping you from working enough. The disability requirements are the same for both and they determine which/what you qualify for when you submit your one application.

I would go see a disability lawyer, because of your age, see what he has to say. It sounds to me like you do not have a clear enough, long enough history to qualify as disabled.