Missed period 9 months after tubal

I dont know where to post this. I had a tubal ligation 09/18/19 during c-section. I've had normal 7 day cycles since. Dr and nurses say it shouldn't effect my cycle but I missed my period last month. Its getting close to me missing two cycles. I've taken pregnancy tests and they're most likely negative/evaps. So I don't think its that. And when I called to get a check up at my ob the nurse was just laughing at me the whole time saying "you can't get pregnant haha, you should be happy", I never once mentioned pregnancy. But I was wondering if any of you ladies have been in the same situation? Did your cycles return back to normal? TIA