A few thoughts for you... First, some people start menstruating while breastfeeding (I started my period at the normal time within one month after giving birth, although I breastfed exclusively. I was still breastfeeding when I got pregnant the second time.)
Some people get pregnant while still breastfeeding even if they aren't mesntruating yet.
So don't depend on your menses to tell you whether or not you are fertile. Although the chances are a little harder that you will be more fertile after you finish breastfeeding and start menstruating. It takes a lot of energy and nutrients to lactate.
-tea- (labor and delivery nurse)