If you prefer to go the natural route, two books may be helpful:-

http://www.babycenter.com/404_will-my-menstrual-cycle-be-regular-while-im-breastfeeding_2610.bc

If you prefer to go the natural route, two books may be helpful:Breastfeeding and Natural Child Spacing, by Sheila Kippley and Your Fertility Signals: Using Them to Achieve or Avoid Pregnancy Naturally by Merryl Winstein. Both are available through the La Leche League catalog.