Ah normal lang yan sis, especially if EBF ka pa for the first 3 months kasi lactational amenorrhea talaga ang nangyayari, a few of us mums experienced the same thing din, walang period for months even with IUD in place! Since mixed feeding na kayo ngayon, the period might come back anytime soon or it could take a bit longer pa, but definitely check with your OB just to be sure everything's okay with the IUD placement and ganyan, para mapakali ka na rin.