Aiyo, constipation dengan formula milk memang common masalah, a few of my mum friends also had this issue with their babies. Honestly, it depends on the baby lah, sebab some tolerate certain brands better, ada yang ok dengan Aptamil, ada yang prefer S-26 or Enfamil. Tapi best thing is to check with your pediatrician dulu, dia boleh refer formula yang lebih gentle for digestion atau maybe adjust the ratio air-to-powder, sebab sometimes itu je yang kena. Kalau baby punya, make sure they're drinking enough water in between feeds also, and jangan lupa massage perut dalam clockwise motion, memang helps!