Bleeding during sex!! I’m scared

On yesterday, me and my boyfriend had sex and it’s definitely not our first time . I ended up bleeding 😭 it was fresh blood and I thought it was my period but I’ve had no symptoms, and the bleeding stopped. I’m kinda scared to have sex again bc of that. What do I do? Most importantly, WHAT COULD IT BE? ( I just turned 18 and have never been to an obgyn)