Charting you temp and watching your CM would help you recognise the return of fertility.
My periods took about 18 mths to return after each baby (I continued BFing through pregnancy, no worries). My sister fell pregnant first egg (so no periods, and bfing, about 18 mths after baby). I know of woman whos periods returned sooner, and other later...so it is very hard to say when it will be for you. But being aware of your CM can help alert you....or you could just enjoy each other, and later nature take it's course! Good chance you will achieve this before 40.
Its unlikely you are ovulating regularly and not having a period. Although in saying that you will ovulate before your first period mostly so you could already be pregnant and not realise unless you test for pregnancy. My Dr put me on the pill for my period to return as DD was 14months old and it did work. AF returned on it and then I went of it. I weaned DD at 2yrs I didn't fall pregnant with this pregnancy until she was 3.5 so over 2yrs all up. Maybe even drop one feed will help encourage AF to return again.
Bookmarks