I also had a bad experience with miralax...it produced alot of heartburn for me. I also have gerd along with IBS-C. I tried taking it for a few days, produced heartburn on the second day; I quit and tried it again in a week and the same thing happened. It took me two days to get over the heartburn. LIke you, Zelnorm worked the best for me. My doc has me on Amitiza, and it works pretty good for C but the side effects for me are strange. I have energy but at the same time I feel a strange tiredness in my eyes and body. I don't sleep good taking it. I hope something comes along that was as good as Zelnorm.