Hi there! Welcome to Healing well!
I'm going too give a go at explain some things of your post. Hope some of it helps! The best advice I can offer though, is speak too your child's paediatrition. Don't feel silly for asking the questions, as at the end of the doctors can't think of everything all at once, and it may be something they have missed, that could help your son.
There are milder forms of CF, as everyone acts differently too the CF gene, and also, yes it can effect some parts more than others. I know of some people with CF, who aren't affected by bowel problems, and don't need enzymes, some people only need 2 enzyme tablets with meals, some need 20.
Has your son been tested for CF, or had the guthrie heel prick at birth? The only way you will be able too know for sure whether or not your son has CF, is with a test. CF itself has a very wide range of symptoms, and just having a couple of similar ones doesn't exactly mean CF.
To my knowledge, constipation isn't particularly a symptom of CF. People with CF who do have digestion problems, have the problem of loose, greasy stools. This is because they cannot digest fat. The only time constipation comes into it, is when too many enzyme tablets have been taken, in my experiance.
Another common symptom of CF is salty skin. I believe that people with CF sweat 100% more salt than a normal person would.
CF does come with other complications too, but all would have to be tested and found by a doctor as they aren't visible.
I hope that your son starts too feel better soon, best wishes for you and your family!