Exclusive breastfeeding (meaning no supplementing and no pumping) offers the same protection as the pill in the first six months post partum (99% effective). This is called Lactational Amennorhea, or LAM (meaning you DO NOT have your period). If you have your period within that first six months, then LAM does not apply and you likely are fertile. After six months, the efficacy goes down mainly becasue baby is introduced to solids and is nursing less. Being that your son is two years old, he is likely not nursing enough to cause LAM. I personally don't think you need to wean him completely in order to get pregnant. If you are not having regular menstrual cycles yet or are having a difficult time getting pregnant, then it may be due to somehting else, but it is not likely the breast feeding, given your son's age.