any ideas what this could mean?

My last period ended on April 15. Ending of April-mid may was very stressful for me as I was going through finals and moving out of my college dorm. May was also the last time I had sex, which we used a condom everytime (about 4 times). I figured I was going to skip my period in May. However, it's not June and still no AF. I had old brown blood this past week with small clots. Could that have been my period? It was very very light, only enough for a liner. I'm starting to get a little worried. Could this be from all the stress I've been having or could I be pregnant? I have no symptoms of pregnancy either.