Bleeding during sex

Hi ladies, I was having sex with a guy I sleep up with regularly when we changed positions and something just didn't feel right, it was just too wet down there. I hadn't had any pain or anything like that but we were both absolutely covered in blood and now for the last few days I've had to wear a pad because I've had a fair bit of spotting. I wasn't due for my period nor do i have it now. Has this happened to anyone else? Do you have any ideas why it happened?