It depends on how soon you want to get pregnant and how regularly you're ovulating (if at all). The best thing to do is chart your cycles (read the book Taking Charge of Your Fertility
by Toni Weschler and check out FertilityFriend.com
for helpful info and tips), so you'll know where you stand -- whether you're ovulating, how frequently you're ovulating, how long your luteal phase is.
I've been charting the entire 15 months I've been breastfeeding, and it would have been impossible for me to get pregnant before my baby was 13 months old. I had fairly regular periods, but my ovulation was sporadic, and when I did ovulate my luteal phase was too short to sustain a pregnancy. Charting is the only way to know whether pregnancy is possible in your specific situation.
at 11:34 AM on Jul. 15, 2010