Help!!!!

What are the chances of me being pregnant because I am having a nervous breakdown.

My cycle length is 28 days.

Had sex on the 5th day of my cycle which is the day after my period. Not sure if is a mind thing but from the vex next day after unprotected sex I felt as though I am pregnant and my tummy is slight growling, I feel like I need to pee often. Could I be over reacting?