Period triggered by sex

So I’m wondering if anyone else gets this? Should I be concerned?

Every time my boy and I have intercourse I get my period after (like the whole week, cramps and all)!

It is almost immediately after we finish too.

I am on the pill, and I make myself get my period every 2-3 months or when I can be bothered. Even if I only had my period a week before, I still will get a full blown period after sex!

I have had a Pap smear and sti tests in the past few years for different but similar issues, but never directly mentioned this to the doctor (my issue always used to be pain and swelling which I don’t really get anymore)