I've had an appendectomy in the beginning of January (I'm 27). I've always had "some" issues with my stomac and bowels due to hormonal issues, but never anything serious enough to interfere with my social life.
But now my digestion has completely changed. If I do not drink 2 liters of water a day, I will not be able to go "number2" the next day or little will come out in several tries and it will indeed feel just like you described: as if I "have to go" all the time. (if I do drink 2l/water/day the next day "to compensate" the annoying "having to go feeling", the day after, I will have to go more than once in the morning, and it will come on very sudden and will be extremely urgent...)
When I do stick to this regime of drinking the water DAILY however, my bowels react the same way as Piercec2's: I have to go once after I get up and it really does feel like it empties your bowels completely. Again it's the same deal: once the urge is there in the morning, I really do HAVE to go and it will be very, very urgent. If there's no toilet in the imediate fecinity, I will get serious cramps and will break out sweating and such, not enjoyable at all. I've remedied this by starting my morning by eating a little yoghurt, that tends to "activate" it all so I can go when I'm still at home.
The only "reason" for this that I can come up with is the following: food remains in the appendix and "rests" there for a while, this will create certain bacteria that help the bowels digest their food better (they are the same bacteria that make the food "rot" and inflame your appendix when food get's stuck there too long...), when the appendix is gone, less of these bacteria will be created in your bowels and hence your digestion will not go "as smoothly" any more.
I've also noticed that I have an urge to eat "more" than I did before and a slight tendency to "over eat" myself, perhaps less nutrients get absorbed in the system of a person that has had an appendectomy as well. This would also explain the "looser" bowel movements that piercec2 described and that I also have since the operation. When faeces look like that, it usually means not all the nutrients have been taken out yet and they were passed out of the system too quickly.
This is why I also started drinking "sports" drinks in between and take extra vitamins (water solvable ones) now. I've just started this, so I can't say a lot about it yet, it does help somewhat, but I hope it will keep on improving and the cravings and over eating end.
So my suggestions:
1. drink at least 2 liters of water spread out through the day on a DAILY basis (buy yourself a convenient bottle you can take a long and refill. I use 1 liter bottles and I also use the "brita" filters so I can filter the water from the tap, coz drinking store-bought bottled water all the time can get really expensive when you drink 2l a day
2. before you "get out of your home", eat something that will activate your bowels (yoghurt, a banana, something with fibers, etc) so you can go before you leave
3. not sure about this yet, but I'll add it anyway: try adding some water solvable vitamins to your diet and drink "sports" drinks on top of your water to help your body get what it needs
I hope this will help your son a little and you guys can stop going to doctors since I believe it's just a matter of getting used to this new state of his body and finding a way to make it work.
I also use jin shin jyutsu hand holds on my body when I get cramps (have also been very disapointed by medical world, hence I've been looking for alternatives for over 3 years now, some work, some don't

JinShin defenately does for me.) Putting both your hands in your loins calms down your stomac (easely done by putting hands in pockets

).
Mary Burmeister is the "source" to go to when it comes to english books, I don't own any of her books, but have looked into quite a few of them at a friends house and they looked very good as well (I only picked the german one coz it's so tiny and I can take it along) :