What Causes A Scanty Menstrual Period With Stomach Cramps?

Hey, about two weeks ago I messed around with a guy and his penis rubbed the exterior of my vagina, and pushed against it but didnt go in. He did not ejaculate. I was about 3 days late on my period, and when I did get my period it was only 2 days, when normally it is 5 days. I have had more cramps than usual, more gas, and more discharge.. I took a pregnancy test the day after my two day period. Could I be pregnant? Or could this be due to stress?