Paranoia getting the better of me! HELP

My boyfriend and I have been together 5 months but had a thing for a few months beforehand also.. I am 17, he is 18 and I'm thinking we will have sex for the first time soon enough.. We have talked about it and it's clear that he wants to and I do too but he is happy to wait for when I'm ready as I'm a virgin but I'm just so paranoid about getting pregnant. I am on birth control pills and we would use a condom also but I still worry so much. I worry when we do anything, just making up extremely unlikely circumstances of how I could become pregnant.. How do I get passed this?! It's killing me😞