TMI- bleeding after sex

Sorry to gross anyone out. But this is really bothering me and I hope I'm not the only person this happens to well, hopefully I am bc it sucks, but hopefully not so I can try to understand this better. Does anyone else bleed after inter course? It doesn't happen all the time. My Dr can't seem to find a explanation except for sometimes you just bleed! It's scary bc were 3 days POV. And trying really hard to conceive. So hard we skipped sex to avoid this and used the stork otc. But I caved and now I'm bleeding ugh. I'm scared that if we did the bleeding would be a problem. I have a cyst on my ovary but my Dr says that wouldn't cause it. My husband is a fairly large man. Idk if that could be the problem. Does anyone else have this problem? It isn't always so it's super confusing.