I Have A One Month Old Who Just Turned One

I have a one month old who just turned one month 2 days ago and we switched her from similac sensitive because she was throwing up to much to gerber soy. Now she's really constipated gassy and cranky all the time. My doc told me pedialyte but it's been three days and no change really in her poops other than shes poopin twice a day but still constipated. I don't know what to do anymore