Late period!!

I am almost two weeks late on my period, last month my period was very short but normal flow...Im usually 28 day cycle and they last 5-7 days. Two weeks ago when i was supposed to start my boobs were hurting and since then I've been cramping on and off...Ive taken 3 pregnancy test and all were negative. I keep feeling like i have started but when i go check its just clear discharge. Has this ever happened to anyone and could give me any advice as to whats going!? Thanks!!