Postpartum period

So I’m 9 months pp. I have PCOS so my periods have never been “regular” but before I had my daughter I’d have one every month or every other month just not when I was supposed to. Well after I had her, the first 5 months I had perfect periods literally on time only lasting 5 days and I could actually track them because they always started on the 4th. However, now it’s been 3 months and I haven’t had a single period at all not even spotting and I’ve been having a lot of pain in my stomach. I’ve taken pregnancy tests and they are negative. Should I go to the dr or is this pretty normal after a baby?