ANXIETTY

This is going to sound dumb but whatever haha. I have been sexually active for a little over a year and I am 18 and have only been with my boyfriend of 2 years! We use condoms everytime and he doesn't even cum inside the condom, when he's getting closer we usually stop and I finish him off. So pretty much, his cum is never near my vagina and I know theres 100282% chance of not being pregnant but I still for some reason get worried about my period coming. I know I'm not the only one that thinks like this so I need some advice. I don't know why I feel like this. My boyfriend and my bestfriend tell me I need to chill since we alll know that I'm okay and just over-reacting but I just don't know what to do. I also know stressing about it can make everything worse so I try not to stress too much.