What Causes Stomach Cramps And Nausea While On A Depo Shot?

Hi, I have been on the depo for about a 1/2 years now. Lately, for the past few days ive felt nausea, cramps on the left side of my stomach and i break down crying alot over little things and my mood swings are very different. I have taken one pregnancy test and it came up negative and havent tried another one since. I am not sure if i am pregnant or not.