Please help!

Ma
So i had my son 10 months ago i was bf and using formula well i got him off the bottle about 3 or 4 weeks ago and been just breast feeding and i havent got my period i was getting it normal around the same time everymonth but since i stoped the bottle i have no period i took a hpt and it was (-) can somone tell me 😒why i dont have my peruod yet please???im not on any bc.