I'm scared I might be pregnant

I'm careful. I'm always careful. I make sure that my partners are tested and show me their results. I make sure they have condoms too before we have sex. My most recent partner (last night) have been together for a week and decided to have sex. He had been tested before we made our relationship official and we used a condom. He's rather big and confessed he hates condoms because they pop off of him or squeeze him too tight. He and I were having marathon sex and in between I would give him a blowjob. Between sessions we forgot to put a condom on and he came inside me. I didn't realize it until I went back down to pull off the condom for him. I'm used to men who insist on condoms but he was totally chill with coming in me. I have an IUD and am on my period but I'm paranoid I'm pregnant. Should I take Plan B? I searched online and it said that taking it won't do much given that I'm already using an IUD. I'm 22, one semester away from graduating and I'm panicking. My parents are super religious and don't know I've been having sex. I'm terrified.