(TMI) Menstrul Cycle Help!

I began getting the DEPO shot about two years ago. At first I didn't get my period , but then I began to get it once again. They're very light (My doctor discussed that with me) but after my period ends , which it only lasts for about a day or two, i have discharge for about 3 weeks and it is very frustrating. I have to continuously buy liners because it will stop for a couple of hours and then start all over again. I don't know why .