Period was due on monday, now its thursday and no period. but light cramping less than usual, sore breasts more than usual, could i be preg? test tom?

Yes and yes: If you do not get your period soon, it would be reasonable to do a test.

Possibly: A stressful event causing diarrhea and headache could cause a hormonal imbalance which could affect one's menstrual cycle. Having unprotected intercourse prior to ovulation would make pregnancy a possibility. A homepregnancy test if positive needs to be followed by a visit to an ob/gyn for an ultrasound to comfirm pregnancy 5-8 weeks after the last menstrual period.