Well, I have gotten pregnant twice while nursing - my DD nurses a LOT more than your son does though. So far no sticky babies though. Usually nursing causes your luteal phase to be too short to sustain a pregnancy, but it really depends on the woman. My first m/c was due to short LP, my second was most likely chromosomal so it didn't have anything to do with nursing. It can take up to 6 months for the normal healthy couple to get pregnant, so 3 months isn't that long. Keep trying, I wouldn't worry too much. Also, there is a TTC while nursing thread on here, come and join us!
Rachel, wifey to (3/06), tandem nursing mama to(7/08) & (4/11) and missing (7/09, 2/10, 7/10)