Close to period date

So for some reason when I end up having sex with my SO near my period start date it's like boom insta period afterwards. It is a bit embarrassing sometimes, mostly if he ends up pulling out with a bloody dick. It hasn't happened often just recent enough. I feel so sorry for him when that happens. One time he was going down on me and fingering and he pulled out his finger and what do you know blood, the poor guy nearly threw up on the bed right then and there.