K.M.
This happened to us, too. It was because at that age he was growing quickly, and when his weight changed his dosage needed to change. We also has to play around with the number of times per day he took the Zantac. For example, they took his dosage and instead of giving it 2x/day recalculated it to 3x/day, so he got a lower dose each time but a got it more often. That made a huge difference, too. It didn't get better until about 15 months, but then it seemed to disappear overnight! There is a light at the end of the tunnel. Hang in there.
K.