Nutramigen was so constipating for my son. He gets one serving of formula a day and just from that (using the RTF Nutramigen), after 4 days he was so constipated he didn’t go from Monday to Saturday! WE, too had to help him using a suppository. We went back to Alimentum (RTF) and it was great. Then we tried powdered Alimentum and it was horrible — he threw up more in the 3 days we used it then he had for weeks. So, we’re back to RTF Alimentum and it seems ok. He’s doing as well (which isn’t well – LOL – as he’s ever done).
So, my opinion is the liquid Alimentum is the best, but I’m sure others have had different and/or opposite results.
Good luck.