Constipation on Similac Total Comfort 1

Kareena

Hi All, my 6 week old is on Similac Total Comfort 1 for 5 days..he can't poo himself..he needs the help of a suppository and his poo is always green and mushy. I took him to his paed and he mentioned green mushy poo is still constipation if he can't poo it out himself. He is gassy and grunts and cries like his in pain trying to push out the poo, that's when I put a suppository for him, which is once a day. Is this normal? Has anyone experienced this on Similac Total Comfort? He also struggles to burp at times and has abit of reflux. If all of this is happening on Similac Total Comfort, is it normal and he needs to adjust to the milk or should I change his milk?