I fell pregnant with DD#3 when Dd#2 was 9.5 months old. Had not had AF post partum. Was breastfeeding about 4 times a day. So whilst my body released the egg and was gearing up for what in most cases turns out to be AF, we just happened to DTD at the right time and i fell pregnant.
I noticed a change in my milk supply, DD also became fussy at the breast. That was prob the only change i noticed......i was prob around 5wks when i found out - due to extreme tiredness i tested and it was a BFP.......

This time i fell preg with bub#4 after having 3 AF's. Werent really trying....werent using contraception either. Ive been told im pretty fertile anyway.

I found i couldnt rely on CM.....i had virtually none i found in my last 3 cycles.....

Good luck......it certainly can happen whilst breastfeeding, and no AF, so dont loose hope !!