Having Cramps, Nipples Darker Than Usual, Hunger. Taking Birth Controls. Pregnancy Test Negative. Reason?

I m on birth control (sprintec 28) and have been since roughly 2011 (for regulating the flow and its heaviness, the length and god awful cramping) but I am having symptoms of pregnancy, I ve been having cravings and my nipples are a bit darker than usual, I ve been sleeping horribly the last few weeks, I m getting irritated more than usual, and I ve been eating a lot. I eat a good amount but then I m really hungry again within an hour and a half, and I ve been more stressed out than usual, but I m not sure why. I did 2 home pregnancy tests but both were negative. last month my period lasted 6 days and a was lot lighter than usual, but two months ago my period only lasted 3 days, when my period generally lasts for 7-8 days and is kind of heavy for the first 2-3 days. this month i got my period (a day late) but its brownish red, looks a little watery and is lighter than usual. What is going on with my body?