SEX/help

Okay. I DONT want to hear how stupid I am. Anyone who is in my situation knows it just happens. Me and my boyfriend just had sex and he went inside of me. I'm on the birth control pill & I am on my FIRST day of my period. I know it sounds gross. But we have been together 6 years. I just need to know. I KNOW it's a possibility of being pregnant but HONESTLY are the chances very low????? Or what?? Help. 😭