Weird periods (tmi)

So I'm taking the Yaz pill. In early April I skipped my period and just went onto the new pack which was fine, in May I got a long, heavy period which I figured was making up for the one I skipped. After that I completely ran out of pills and didn't get a chance to get another script done for about a week, and it made me have another period which I figured was withdrawal bleeding? It was the same as my regular periods which are usually 5-7 days..anyway now being June I got my 'period' on Saturday night but it was really light- like no flow and was mostly just old brown blood, not like a normal period. And it was over by Monday which is odd. I thought it would just pause for a day and then continue like it has in the past. Should I be really concerned or is it just luck that I had a really short period? Could it be a pregnancy thing?