How Could I NOT Be Pregnant By Now 🤔

My boyfriend & I have been together for about 9 months now. Whenever we have sex he cums inside of me. I'm starting to get worried b/c I always expect to get pregnant & I haven't yet. My period always comes. People always tell my I "look" pregnant & I start to think that I could be pregnant & there comes my period once again. I don't understand how I haven't gotten pregnant when he cums inside every time. 🙄