This forum is very slow but very informative. From what you have described, it could be herpes, another STD or just your body reacting to you stressing out.
Most people's initial outbreak is painful with flu like symptons. You did mention abdominal pain and increase in body temperature. Have your doctor look at the "pimple" and get yourself tested. This sometimes is the hardest part but it is the only way to get peace of mind where this is concern.
You should also get an HIV test since you had unprotected sex. There is no getting around that. Then you can deal with the task of taking better care of your body.