Spotting on depo shot

So I've been on the shot for about a month I got it on August 18 and I missed my period for September and this morning I just started spotting. Is this normal or should I be concerned? Yes I'm sexually active but I make my bf pull out and I make him clean up before going at it again. Please let me know if this is normal or I should be concerned!! (I did get my last period before getting on the shot which was July 27th then didn't have one for August then supposed to have gotten my period September but didnt. My period was very irregular to begin with, it jumps a month sometimes)