bad day

I seem to be in a cycle of bad days right now. I took my flu shot a few days ago and I always have a reaction bruising, swelling etc. but where I work it is really needed. Anyway Friday my day off I was in bed with achy joints and bad diarrhea coincidence maybe but a bad day off anyway. Later that night after not eating all day I was hungry and popped a frozen pizza in the oven. To back up a little last year I had a toothache went to the dentist and she said only a tiny cavity easy fix 2 hours later she said sorry but a lot is going on in there and your body is rejecting that tooth even a root canal won't fix it so she had filled it sent me home and a few months later after a lot of pain it was pulled anyway! A few weeks ago I noticed the same tooth on the other side had changed color a little but no pain until I bit into the pizza last night and it crumbled to dust to the gum wow an awful feeling it must be dead as there is still no pain so first thing Monday I will make an appointment to get it removed the rest of the way. I am in fear my body will keep rejecting my teeth. I read up on it it is true but it doesn't say what causes it.