trying for #2 while BF

Has anyone ever exclusively breastfeed and fall pregnant again? We want to try for number 2, but my OB told me that since the baby isn't yet 6 months and is breastfeeding on demand that the chances are pretty low. I'm wondering if I should start implementing formula along with breastmilk to increase our chances. We suffer from fertility issues, and if we can fall pregnant on our own, that would be ideal I've heard success stories from mothers who didn't BF and also had PCOS, and got pregnant again right away after their first child. Yes, we understand how difficult it is to have 2 children in diapers..not looking for that type of advice. Just wondering if anyone has gotten pregnant with their second on their own while breastfeeding exclusively.  TIA