Hi Susan,
It's possible to be allergic to anything. My DD2 actually had a sensitivity/allergy to rice until just a few months ago. However, it sounds like your bub might be getting constipated with it? That was the case w/DD1 - we gave her a couple of spoonfuls and she was sooooo miserable, completely constipated and in pain - we never gave her rice products again until she was around 2.
Were there any other signs? Any rashes, any vomiting, congestion? What about strange stools, either loose and mucousy, or hard and pebble like (hard can be constipation)?
I think that's the issue, of course can't be sure. Glad it helped once you removed the rice and he doesn't show other signs of food allergies!
HTH!
xo