Weird bleeding

Tmi to start. I've had some dark red/Brown spotting and getting cramps and extremely sensitive mood wide. Yesterday the blood got a little heavier but is still that old blood color, this morning its turning more bright red but with like little blood clots on the tampon. I took 2 pregnancy tests a couple days ago as I've been trying to get pregnant but they both said negative and I'm suppose to start my period tomorrow. Any idea why the blood is such a dark color if in just starting my period tomorrow. Also I've been having sex just about every day if that makes a difference.