Irregular AF but back on pill???

After I gave birth I bled for quite awhile....normal. Then it started up again after having been gone for about a week. When I went to my 6 weeks check (while still bleeding) the Dr said AF had returned since I wasnt breastfeeding and so I went back on the pill (same brand as before DS). My next period showed up at the normal time and was normal length (only thing different was I just couldnt use tampons comfortably, but I figure that will get better in time) But now according to my pill, AF shouldnt be due til next weekend....but I started to get spotting yesterday. Its a little heavier today but not what i would call a full flow.

Is it normal that AF would still be abit random after birth, even tho Im back on the pill???