Too cautious?

Hello everyone! I just have a quick question for everyone out there. So I am currently on the birth control pill, have been for years because of acne and heavy periods in high school. I now am in college and have a boyfriend but whenever me and my boyfriend have sex and he ... ya know... inside of me I always feel the urge to take plan B! Is it bad to take plan B when you are on the birth control pill? He doesn’t come inside every time, but it does happen every now and again, ya know we’re just caught up in the moment! plz help (: