Aspirin can cause internal bleeding because it can irritate the stomache - perhaps that is what has happened to you? The fever is a bit strange though - it might mean you've got an infection. I don't think you'd get locked up for it. If you don't take a lot, you could just say you've been taking it daily because you've read that taking painkillers daily can help reduce bloodclots, and you haven't been reading the label and you might have been taking too much.

How long has the pain been going on for? And the blood?