Quoting The Devil's Squeekerz:" I have no idea unless it's because I still breastfeed. I didn't think breastfeeding would screw it up when it's no longer exclusive though. "
My oldest was 3 months when I started giving him formula and breast feeding. I didnt get a period until he was 8 months when I stopped nursing all together. My youngest was 16 months when I stopped and didnt get a period until after that. She didnt get formula, but she ate food and drank milk and stuff after a year. I only nursed her at night at the end and still no period until I stopped completely.