Constipated baby

Any tips on helping my newborn with constipation? My baby is 9 days old and I’ve been using aptamil. He was on the pre-made formula for the first 3 days due to being in hospital which he seemed happy on, but once I got home and switched him over to powder formula he has been really constipated. I fed him on ready made for 24hours again to see if that helped him but it didn’t, so I started adding some infacol and I’m now trying colief drops to see if it helps him digest the milk better. Midwife appointment tomorrow so will ask for their advice, wondered if any other mums have struggled with this?