Period gone.

My baby girl is almost 9 months (will be on the 30th) I had my normal PP period "bleeding" for 2 months then didn't have one for 6weeks till I started my birth control, it was normal for a few months then when I stopped talking birth control my period stopped too. It will be 3 months or so now that I haven't had a period. I've taken a pregnancy test every month but it still is negative. Not trying to get pregnant so SO and I have been using condoms a week before I stopped taking my birth control. Also not complaining but damn.. why did it just disappear like that? This is my 3rd child and this has never happened to me before. Has this happened to anyone else?