1 month old constipated

So I’m needing help my son is going on 3 weeks as of Thursday and first day at the hospital even second day he was doing great with poops but when we got to the home he went days without pooping and would poop little to none he was on gentle ease and occasionally breastfeeding spoke to his pediatrician about it and she put him on the Réguline she said to give it least 24 hours and see if it made a difference well it still hadn’t he was still having trouble pooping it was a little more then before but still was I told her she said okay to give it at least two more weeks but he had gained weight so she wanted to see just how much longer wel it’s still the same way and now he’s on the regular infant enfamil formula the yellow can and 24 hours in and he’s already had a good enough poop with all this extra information anything else I can try besides switching formulas I don’t want to keep switching back n forth I feel like it’s going to harm him or mess with his stomach even more