pregnancy scare

I had sex on the 17 which is when I first began my fertility week! I didn't know I was fertile until I downloaded this app! My guy said he didn't finish inside of me, which I saw him pull out; but his penis went limp inside of me a few times! I don't know if that was because he finished in me or what! But it's been a week and I'm cramping in my bladder area! I'm scared I might be pregnant can someone tell me what to do!