What Does My X-ray Test Report Indicate?

My son had an xray done when we went to hospital complaining of stomach problems such as nausea and some regurgitation. He takes prevacid daily but it didn't seem to stop the issues.
The xray showed he was extremely constipated, even though he has daily bowel movements. So he was prescribed some liquid in a big brown bottle and said that it should do the trick. He had it for about weeks and we never noticed any big difference however he no longer complains of feeling sick after eating. My son is 8 yrs old he weighs 79 lbs and he has ADHD. I was doing some research about there being a link between constipation and ADHD. Is this something you are familiar with, and does this mean I will have to keep him on some type of laxative long term?