What Causes Irregular Menstruation After Giving Birth To A Baby?

Hi i had a baby 9 months ago and went on the pill when she was 3-4 months after i had my first period but kept getting what seemed to be my period every 7 days stayed on pill for about 6-7 weeks but still kept happening so took my self off the pill. Now I haven't had my period for 3-4 months. I'm not pregnant and put myself back on the pill about 3 weeks ago