Period pains or something else

According to the app I’m due on this Saturday, however, last Saturday night I had an incident with sex and a condom. Basically I’m not sure if he finished inside of me or in the condom and then it came off after. Yesterday I had bad cramps and today I’ve got really bad belly ache. I never usually get period symptoms or I do but I never take note of them like this. Do you think bad belly pain is a sign of period or do you get pains like this when you have conceived?