My son who will be 3 in August is on this also for chronic constipation. It works very well and is much better for long term use than laxatives like milk of magnesia because it doesn't have all the metals, etc that those laxatives have. It may just take a little while to figure out the correct dosage. I started my son with half of what was marked on the dosage cup, so I believe he was getting 8 grams once a day in the morning if my memory serves me. I've since cut that in half. The advice my doctor gave me in adjusting the dosage was to give any adjustments 2 days to take effect. He said that it would take the body that long to adjust accordingly. My son was supposed to be on it for 2 months which would have ended this month, but the doctor advised us to continue it through the summer since we tend to be less hydrated in the summer due to sweating, etc.
So have no fear, it's been working great for us and probably will for you too. I just hope my son gets past this. We're attributing it to him holding it in too long, but of course we don't know for sure if it's more than that or not. We've been having trouble with potty training because of his constipation but hopefully it will all pay off soon. Good luck to you!