Acid reflux

My son is 9 weeks old and suffers from silent acid reflux dr for 2weeks put him on Zantac and while he did good he got rash all over his face and got constipated. Went to dr and she told me for 2days to stop the Zantac as it would take 48hrs for it to get out of his system and if it did cause the rash for the rash to clear up; well it did but now my baby is in pain again so dr said to call her if symptoms returned and she would put him on a different medicine nexium; has any one tried nexium. I'm scared to try another medicine but my baby is in pan