What Causes Vaginal Discharge And Abdominal Cramps?

Hi,
I am 28 years old and TTC. I got my last period on 5th feb...but after ovulation period on 26th feb got bleeding which was like red in white discharge..then next day got light brown discharge and the third day got lumps of black discharge ...but everything happened for one time for a day...after dat started to get white milky discharge...somtimes feeling cramp in abd...recently felt firmness near left side of belly button. now its ok and feeling hungry and sleepy often..took a home pregnancy on three days back...it showed negative...wats going on to me...