Why can't I get a student loan?

I've applied for a Student Loan with Sallie Mae several times with 3 different cosigners and for variable amounts. I must have applied at least 6 times and got rejected every time. both of my parents have lousy credit, but I was under the impression that my aunt had good credit. I applied many times using my father, a few times with my stepmother, and once with my aunt. Did I get rejected with my aunt because I had applied too many times before? Also, I've already filled out my FAFSA, and can't get any other government loans, which is why I need a private loan.