Exhausted With Headaches And Heart Burns. Why Was I Bleeding?

I had unprotected sex mid cycle. A week later I had exhaustion and headaches and heart burn . A few days later I had period pains, but not severe, then my period came a few days early, but was very light, mostly just when wiping and dark brown, then rusty red then pink then dark brown again. No clots at all. Am usually very heavy with bad cramping. Since then I have been increasingly nauseaus, can t keep anything down and now feel very bloated, and like I need to pee. Also the veins in my breasts have become visible. Got BFN on HPT around when my period was due. What could be the problem?