Anyone else experience this!? HELP!

So, my partner and I have been sexually actice for a couple years now. But just because we're "experienced" Doesn't mean we know everything. Like for example, I've started spotting after sex.

At first, it would be little bits of red and so I chocked it up to swollen and torn tissue. Nothing to worry about, right? We'll just take it easy next time. But almost a week ago, after a second round I started to spot. Not normal little bits of pink. But gross brown gunk and blood. Period style. I'm on the pill, and so my periods are very controlled, and I am not due for another anytime soon.

Of course I've gone down the google whole and scared myself shitless. Is it a sexually transmitted disease? No, my partner and I were each other's firsts, very monogamous, and we've had our shots. Fibroids? Tumours? I had a check up in July in regards to fibroids and growths, with everything coming up daisies.

The thing is, its been nearly a week since, and I'm still spotting brown gunk.

Help.