What Causes Vaginal Spotting With No Regular Period?

Around the time I was supposed to get my period I started spotting but I normally have a regular period with a regular flow. This went on for about a week. Then I started feeling really tired an nausea at night an some in the morning. My breast an nipples are sore an tender Ive been goin to the bathroom more often an I think I could be pregnant, but I have taken 2 home pregnancy tests an went to the hospital an had one done all neg. Im not sure whats goin on..