I have a terrible tooth abcess and started antibiotics monday. is it normal to get worse after 2 days of medicine?

No unusual: Most antibiotics starts working 48 hours after taking them. Once a infection starts its like a bell shape curve in a graph. It depends upon where you catch it / at what point. If you come in when the infection is starting to increase in discomfort chances are the antibiotic may take longer before it starts working.

Yes: I would see your dentist as soon as possible. The abscess should begin to decrease by the third day; if this does not occur you may need to change antibiotics.

Tooth abscess: Pain associated with a tooth abscess is do to pressure by the expanding abscess. If you are already seeing a dentist and he has started root canal treatment and placed you on antibiotics, the pain will usually start to diminish after antibiotics start working to reduce pressure. If pain does not stop your tooth needs to be reopen to reduce pressure or the antibiotic needs to be changed.