Unprotected Sex with Birth Control (Please Respond!)

The past couple times I’ve had sex, the only form of protection my boyfriend and I have used is my birth control (daily Tri-Sprintec). I never miss a pill but I can’t help but worry that I may be at risk of being pregnant. My period is supposed to start in a couple days but my anxiety won’t let me ignore it. The last time we had sex is what’s really worrying me. It was Saturday and he ejaculated a lot. At that time in my cycle I had a low chance of getting pregnant and I took my pill shortly after. Any advice? Does anyone have any input or stories that may decrease my stress or help me figure out just how big of a risk I’m at?