My LO is 2 months and is on formula and bf. He had not been pooing for 3 days is it normal? He keep make shitting sound I don't know should I give him a bit of plain water..

he seems constipated. as he is still young. do not give plain water or any prune juice. What you can do is to do some stomach massage for him. hold his knees together and go into a circular motion over his tummy. It will help to promote tummy circulation

Actually when they are two months old they shouldn't get constipated so easily as they have not started on solids too. Consider to change his formula. What brand is he on? I will give a little Plain water but not too much

It's pretty normal for them to not pop. I know if doctors who said every e years old don't pool daily.