Depo shot in February..?

I got a depo shot February 12th and I was due for another one on the 12th of may. I didn't go get it because I didn't like the side effects. I've been bleeding ever since the shot wore off. Its been blood and a brown discharge (TMI I know!) Sometimes its alot and other times its just the brown discharge, other times its both and other times its nothing at all. Its very confusing to tell whether my period is trying to come back or if there's something seriously wrong since its been happening so long. Also, I've been having unprotected with my boyfriend of 2 years (it couldn't be a STD because we both got checked and were both clear) so could this be a sign of pregnancy?? I've been wanting to get pregnant for a while now but got the shot only until I finished school. Is it just my period trying to get back to its regular routine? Has anyone else had this happen?? Is this normal after the shot wears off?? Should I be more concerned?? HELP!!