Can I check if anyone just change from nan 1 to nan 2 and baby cannot finish drinking and have difficulties to poo and he poo abit by abit ?

I read that for formula milk, stage 2 formula will have a higher iron content than stage 1. If you have recently made the switch, reckon that the higher iron content could be the reason why baby is having a harder time passing motion. His system is still getting used to the change, it will pass eventually. If you're already feeding baby solids, perhaps you can increase his intake of fruits and veggies to help things move along down there.