What Causes Delayed Periods With Discomfort In Breasts And Dizziness?

I quit taking birth control (Depoprovera) in September 2010. I had a period in January 2011 that lasted 3 days but not since then. The past several weeks I have had 'fullness' and discomfort in my breasts, mild back pain, dizziness, the 'shakes' (mainly when I go a longer period without food), cramps, hotflashes, and have recently noticed that the top of my stomach is protruding and hard. I occasionally get "butterflies" that I put off on gas. Lately I've been getting a 'fullness' sensation in my stomach which has decreased my appetite but i'm still gaining about 2-5 pounds a month. I have taken a pregnancy test which was neg. Should I be concerned of a more serious problem.