Is Period Affected Due To Taking Depo-provera Shot?

I had a baby almost a year ago. At my six week check up I got the depo-provera shot. I used this as a birth control for six months. My periods became lighter. I decided to stop using this method of birth control. After stopping my periods became extremely light and there was barely and blood but I had grey, tissue like stuff coming from my vagina. Now I haven't had my "period" for two months. Should I be worried or do you think it's just after affects of stopping the shot?