How long can first period lasting after stopping depo injections?

I had depo injections for two years - no periods at all during that time. last injection was due mid-March but I decided to stop and my period arrived three weeks ago (so 7 months since last injection). Problem is, it's lasted three weeks. Not really proper blood - often dark brown, very light, not free flowing blood, just kind of like "smears". No pain or cramps until today, my stomach feels bloated and crampy but I've been really tearful and irritable. Haven't been to doctor yet, as I've kept thinking it was stopping. Getting a bit worried now though- anyone had similar experience? I'm 43 and periods before depo were always regular, fairly light and lasted about 5 days.