I second the short luteal phase as being a possible issue while BFing. I was lucky (not), to get AF back 4 mo postpartum while exclusively BFing. I could feel it when I was ovulating it was much more obvious than before I had a baby. One of my friends who almost never ovulated on her own, said she also noticed how strong her ovulation pain was after having her baby, and surprisingly her cycles went from completely unpredicatable, to exactly 28 days. Now, I had short LP problems while trying to get pregnant with my son, I had to take bromocriptine for elevated prolactin (I was obviously not nursing). The bromocriptine did help increase my LP, but since I am nursing, I cannot take bromocriptine again, and I also had to take clomid/progesterone last time too, b/c I don't think my egg quality was that great, and I had consistently low progesterone levels. I have suspected for the past few months that I have been having a short LP again. Whether it has been due just to nursing, or it is a combo of my pre-existing tendancy towards short LPs and the nursing, I am not sure. Anyway, my suspicions were verified, when I started using OPKs last month, and it turns out my LP is only 4-5 days long. There is no way I would be able to sustain implantation with such a low LP. So, even though I am ttc #2 (joshua is 10 mo old), I pretty much have the feeling that there will be no way that I will be able to get pg again until joshua is weaned or at least weaned down to much fewer feedings a day. I am hoping that the second time around I won't need to take any clomid or anything else to get and stay pg.
BTW, good luck ttc!