It is rather common and nothing to be alarmed about. That being said you do need to get those feet in some stirrups for a look. Regardless of what it is it can be taken care of and addressed. It could be something simple as a polyp or a little more bothersome like a chlamydia infection. It could be a little tear from a fingernail or a little abrasion from all that friction. If it is chlamydia or gonorrhea you need antibiotics because left untreated could lead to infertility,
I would recommend you see your gynecologist to find out what's going on. You may have an infection and sometimes that can cause bleeding. Or, if there was not enough natural lubrication there could have been to much friction and that can cause small tears and bleeding. See your Dr to find out for sure.