Help! Pregnancy scare?!

So last Saturday me and my boyfriend were messing around. Usually we always use condoms but we were out. He was satisfying me and I came. I went a peed after and because I didn’t want to get a  Blatter infection. About a hour later we had sex (without a condom) and he pulled out... I looked at my app and realized it said it was my first day of being fertile ( my period are really irregular and I miss months at a time before so it hard to keep track when it’s accurate). At this time the stores are closed so I couldn’t get plan b. The next day I ran to Walmart and got plan b. I took it between 12-24 hours after unprotected sex. It’s now about a week and I don’t feel good and my stomach has been hurting all day. I dont know if I’m just scared or if I actually am. I’ve usually take the take action pill because it’s cheaper but I splurged on the plan b one-step because I wanted to make sire it worked. Im nervous and scared because I’m only 18. I will take a test in a couple weeks but should I be worried??