2 months old not pooping

My 2 month old baby now only poops once every 2 or 3 days. PD says it's normal but baby has been so fussy lately. He used to poop several times a day in his first month. I tried to eat more fibre but it doesn't seem to be working. Baby is on mixed feeding - formula 2-3x a day and the rest are breastmilk. Is there anything tt I can do to make him poop more frequently? #1stimemom