Missing Period 4mo PP not BFing

I had a period around 8 weeks postpartum with my Sept 23 baby and it has yet to return. Not pregnant (i tested cause paranoid haha) husband had a vasectomy confirmed successful while i was pregnant. I only breastfed for the first few weeks. With my other babies when i stoped breastfeeding it came back pretty regularly about a month after i stopped. I know postpartum can be diff every time but ugh its frustrating ive been pmsing on and off for weeks and starting to get headaches and tired all the time now but still no period its about 40days since the start of the one i had around 8wks postpartum. This is my 4th baby anyone else experience this?