Late period…. Pregnant or irregular postpartum

Reduced pumping and now totally stopped the other day. I’ve had 2 periods postpartum, last month and one before, both on time. This month, missed period. Maybe my third postpartum period will just be super late? The last 2 were on time. I did pregnancy test yesterday and negative…. Could it be false negatives? Or just irregular? Should I go to my obgyn?