Billings and Breastfeeding

Hi. I have used Billings in the past successfully but due to being almost nonstop pregnant since 2007, my knowledge is a bit rusty. I am breastfeeding my 7 month old DS (about 5 or more BFs a day but he has recently started on 3 meals a day). I am still waiting for AF to return. DH and I bded the other day and I assumed that because AF has not returned we were infertile, but there is now a little voice in my head saying that I am wrong. So, what are the chances of being fertile and actually falling pregnant? I am going to contact the Billings office to organise a refresher tutorial but they are closed over Christmas. Any info you have would be great.

I think I am freaked out because we fall pregnant very easily, and we wanted a little break before trying for our next baby.