Your first step is to contact the financial aid office at your college and see what they can tell you about the situation. They should be able to help you sort out the types of loans included in your FA package. Aside from the questions you have about your dad you should know the amounts and types of your loans so you can plan for repayment post-graduation. Your second step will be to get ahold of your credit report to make sure your dad isn’t taking out other credit in your name, such as credit cards or loans. If anything in your credit report looks fishy put a hold on it before talking to your dad. If you find he’s taken out loans or CC’s in your name you may have to go directly to the credit card/loan issuer to resolve the issue.
It’s possible your dad is being responsible about your credit but doesn’t want you to see his tax documents because he doesn’t want you to know how much he makes or how much he’s screwed up his own finances. In any case you deserve to have a good grasp on your financial situation. Good luck.