What Causes Periods Pains With No Menstruation After Childbirth?

Hiya, I had a baby 4.5 months ago and have only had one propper period which came 6 weeks after my baby was born. I have blead 2 other times but they were only for a few seconds and they were very weak. I was breast feeding and taking the pill but I am no longer breast feeding. I also stopped the pill for a while to see if that was affecting my periods but so far no luck. I do keep getting period pains and sometimes feel sick but it has been going on for a few months now. regards, Keeley