How To Stop Bleeding After Depo-Provera Shots?

Hi. In the last 5 months I have recieved 2 Depo-Provera shots. I had been spotting and bleeding after the first shot but did not think much of it as my doctor had warned me this was a side effect and told me it would stop after my second injection. This has not stopped, although it goes away, it always comes back and I never know how long for. When I spot sometimes it is brown (old blood?) but it only happens during the day and goes away at night. I am very concerned, what do I do?