Mirena and really screwed up cycle...?

Okay, so I got my Mirena out in september because I didnt like how the side effects affected me... I had a normal period september and october but then my period that was to show up in november showed up the 23rd, which was 3 days late and only lasted 2 days. I took numerous pregnancy tests and they were all negative. Well it hadnt even been 3 weeks since my last period and I started bleeding again. Im going on day 3 now, and Im just really confused why my periods are this messed up? I had mirena for a year and had periods that lasted 5 days and came monthly like clockwork. Every 28 days and always started first thing in the morning.... Before I had mirena they were consistant too. Is it possible that I couldve been pregnant and miscarried or is my monthly's just this screwed up?