Period while breastfeeding?

I'm 8 weeks PP and just started on the low dose mini pill for birth control last week. With my firstborn I breastfed also and didn't have a period for a year. This time I am spotting and cramping. The baby is breastfed most of the time but for the past week hubby has given her a bottle at least once a day. Is this a sign that I'm not producing enough milk? Have any of you other mommas had your period start back so soon while breastfeeding?