Post partum menstrual cycles?!? Should i be worried??

Hey guys, its me again lol. Okay so, I got my first cycle on easter.. I was getting them very close together as I figured was normal since my lo was just born 1/31/16. She is now 4 months old. Anyway, after that, one started again on 4.7, started again on 4.18 lasted about a week, then again on 5.1. I have not had another cycle since the one on 5.1 and I guess what I'm trying to figure out is if I should be worried that I may be pregnant again? Or do you think my cycle is just abnormal and trying to return? I've been on the heather tablet birth control.. I have missed a couple of days here and there but if I miss I take it again as soon as I remembered it.. Anyways, any advice would be appreciated. Thanks in advance guys.