Just got depo, what to expect?

Al

I just got mg first shot of depo-provera 2 days ago on the 4th day of my period. Which according to my gynecologist is the best time to do it. Anyhow, what should I expect for the next 3 months. I go back in February for my second shot. I mean I do expect some spotting but I'm nervous as what normally happens. I'm 16, never been pregnant, and have regular periods that last 5 days and happen approximately every 29 days. What should I expect?