C.B.
My daughter who is 12 was often nauseous after eating last summer and it turned out she was completely compacted/constipated (from drinking too little all summer). She also had some cramps below her belly button, so not stomach. I thought perhaps she was starting her period and since she is 12 and told me she pooped every day, I did not know what it was. After seeing the pediatrician about 3 times over 4 months (who said "drink more and take Miralax" which did not really help) I asked to see a GI specialist, who took an x-ray and could see that her colon (from where the small intestine feeds into it until the rectum) was completely filled with hard stool. She did poop daily, but later told me it was "pellets" which was just the end of the compacted stool in her colon breaking off and coming out. When we used Miralax over the summer she seemingly would have diarrhea the next day, but the GI specialist explained that food is liquid in the small intestine and was just seeping around the compacted stool in her colon. The colon is where you absorb most of the moisture out of your food.
The treatment was a 2 day clean-out routine similar to when you have a colonoscopy: I believe it was taking 1 full dose of miralax in 8 oz. of water, twice about 15 minutes apart, and then a Dulcolax stool softener, and 24 oz of water the rest of day 1 with only light meals like soup. The same on day 2 perhap minus the Dulcolax and light more solid meals allowed. After about 2 hours the first day she started going to the bathroom hourly and felt sooo much better mid day. Then after the 2 day clean out she is now on 1 dose of Miralax in 8 oz. of water daily. Doc said to stay on Miralax twice as long as it took to get constipated (for a total of about 6 months). She also needs to drink at least 24 oz. of liquid daily, so we bought a 20 oz Camelbak bottle that she takes to school and drinks by the end of the school day. Then some more juice and milk at home and she has been nausea-free since then! Good luck.