Pregnant?

Hi I have been using the pill ever since my baby was a month old. there are times I do take my pill late, sometimes hours and 2 to 3 days late but when I do remember it I take the missed pills. A week after I stopped breastfeeding I had a slight menstruation BUT it was weird because it did not smell anything, and very very slight cramps. color of the blood was dark to brown. after 2 weeks I had slight menstruation again but again it did not smell anything. I already took a PT but it was negative, could this be implantation bleeding or is my cycle just changing since I just had my baby?