I also had my periods dissappear and return on Mirena. My experience was a little different than yours, however. I bled for close to 3 months straight after insertion, had light spotting at strange times of the month for 4-5 months, and then had a very irregular period with breakthrough bleeding. Before Mirena I only had my period 4-5 times a year. The bad news for me was, about the time my period returned all of my weird symptoms popped up as well. I don't think it's unheard of for a period to return, but please keep an eye on yourself and don't dismiss anything else happening with your body. I wish I had paid more attention to my body during this time. It took me nearly a year to discover my declining health was due to Mirena. Classic hormone imbalance symptoms (for me night sweats, dry eyes, and breakthrough bleeding) were some of the first signs.