Periods Early

So a couple days ago I was having sex and when he was in me it started hurting really bad (really bad cramps in my lower abdomin and vagina) so he pulled out and there was brown discharge. Looked it up and said it is common with ovulation. But I took a test and it said there was no Lh surge, now it's 3 days later and I'm still having cramps and I think it's my period because I have a flow. About 2 weeks early, I've been very stressed out lately if that makes a difference. Has this happened to anyone else?? Not sure what's happening with my body. Thanks in advance!