Period post baby advice

My little chunk is 4.5 months old. I had to stop breastfeeding at two months (to long to explain) and I had two normal periods in June and July and then this month nothing. Just did a test and its negative. I've always had regular periods and the first two periods post baby were on time and five days as always. What's going on?! Help. Am I pregnant and I'm to early to test or do people just not get periods randomly after babies? Wth.