any one have this happen?

So my period didnt come last month(its a month late now) but ive taken several test an gone to the doctors an i keep getting negatives. But last night after having sex my SO noticed i was bleeding, i only bled for 15-20 minutes at the most an it was just a little bit. I dont know whats going on im going to call the doctors tomorrow an see if i can get a appointment but i just wanted to see if this has happened to anyone else, please let me know any share experience will be greatly appreciated! Happy holidays!