Hello. I Received My First Depo-Provera Shot Two Weeks Ago.

Hello. I received my first Depo-Provera shot two weeks ago. I was on my period when I received the shot, and am not pregnant (tested negative for pregnancy on day of Depo, during my period); I have not had sexual intercourse since receiving the shot, so there isn't a possibility of me being pregnant. That isn't my concern. My concern is that starting 5 days after I received the Depo, I had sharp abdominal pains. Those pains ceased after two days, but were replaced with daily menstrual-feeling cramps, with light spotting each day. What is going on??