Postpartum Periods

I need some input on this... my son is 3 1/2 months old. I had a period one month ago that was 7 days long. It was heavier than usual and I had more cramps than I did before I was pregnant. I was supposed to start my second period after giving birth 3 days ago. I haven’t started it and I’m not showing any signs that it’s coming. I am on the pill and stopped breastfeeding at 6 weeks (I got my first period about two weeks after I stopped). I took a couple of pregnancy tests (all negative) today because I’m really paranoid and anxious about this. Is this normal? I thought I would skip my first period, but not my second.