Bleeding when I'm not on my period?

my period just ended 5 days ago. I was able to have sex and everything with my boyfriend without an issue.  my labia is very sore and kinda burns to the touch and it has since my period has been over. tonight I went to masturbate and when I looked at my fingers they were covered in blood. I don't think it could be an STD or STI because me and my partners are each other's first. I'm bleeding really bad and I'm super sore to the touch. anyone have any idea what it could be? greatly appreciated, thanks!