What Causes Terrible Back Pain During Ovulation?

The week of my ovulation I had terrible back pain after. 15 days later when my period is due I had brown discharge but no blood no cramps, nothing. The week before my breasts were tender, i felt cramps and then they were gone. The brown discharge was there for 2 days and now its gone. All home pregnancy tests are negative, but i usually get a normal period with heavy flow. never like this. could i be pregnant? My husband and I have been trying for over a year now to get pregnant.