I need advice!!

So I started spotting September 1 through the third very light pink and brown not my normal cycle at all I was supposed to start today my. Normally last four and five days very heavy flow. But I've been cramping this whole month. The last time I had sex was August 29. But I've taken a pregnancy test and I say negative maybe I'm not far long enough to know by urine or not. Does anybody know what's going on? Has this ever happened to anyone I hope I'm pregnant!