I had unprotected sex last Sat its now friday 11/18/16 I'm having this feeling like period cramps but its too early my expected period is on 26 What could be the reason why?

Hard to say. This may be unrelated or you may be showing symptoms of a STD like gonorrhea or chlamydia. Abdominal discomfort is a non-specific finding at best but these two would be the worst things I could imagine.Both can make you sterile.You may want to get in and be checked.