Mumof2boys congrats!!

Nice to meet you all X
I'm breastfeeding my first baby, she is also 4 months old.
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?
DD is an IVF bubba, but I know so many women have fallen naturally after their first.
Have checked out the ABF website but didn't help me very much.
Cheers X