Help!

Hello everyone!Me and my boyfriend were on a Long distance relationship. He came here to visit me and we had "unprotected" sex on July 15. I was so nervous and all that. And btw my period is irregular. But I had a period last July 31 until August 2. It lasted for only 3 days when I usually have 5-7days kind of period. Although the 3days period that I had, its heavy and I used a lot of pads that time. So now I'm just paranoid if there is a chance that I could still be pregnant. I'm not having any morning sickness or something, but just by thinking or being paranoid about it makes me nervous.