My periods stopped immediately?

Hi! I've had the mirena IUD for two months now. I spotted briefly after it was put in, as was expected. The first month, my period came as predicted, lasted only slightly longer, but in general was much lighter. I still haven't had a second period. I know my doctor said that mirena can eventually lead to you not having a period at all, but I thought this was after 3-6 months. Did anyone else stop having periods this early on? (Also, no chance of pregnancy, so I know that's not it!)