Pleaseee tell me what’s happening

So for like the past 3-4 weeks I’ve been sleeping with this guy and every time after we have sex, I end up bleeding or spotting For days. That’s never happened to me before? I was checked by my gyno a couple weeks ago for infection and everything was fine. And I can’t even tell when my actual period is happening bevause it’s irregular. I feel like this isn’t supposed to be happening and I need to know If anyone else experienced it