AF returned 16wks exactly after giving birth, while full time Bfeeding, does this mean I can fall pg again, would I have to stop feeding if I did?
Yep, if you have AF you could be ovulating and could get pregnant. No, you wouldn't have to stop feeding if you got pregnant. Some people feed right through pregnancy and then feed both babies when the little one arrives.

Australian Breastfeeding Association - Breastfeeding Through Pregnancy and Beyond

I am 9 weeks pregnant and breastfeed my 14 month old bub and it's still going ok.