He doesn't hurt in any particular spot, does he? You'll want to be on the lookout for appendicitis, which can cause nausea and, of course, pain (lower right quadrant pain). Gall bladders don't usually go bad in children that young, but they may if you have a strong family history and belong to an at-risk racial group (I have heard Native Americans have a high tendency to bad gall bladders).
While IBS can develop in young children, I think most people don't develop it until early adulthood (there are some here on this board who have had it since their teens, though). You may want to start with a therapist to see if he's literally worrying himself sick. There may be something going on that you have no idea about--a bully at school, a teacher that is disliked, social adjustment issues, learning problems. If stress is causing his problems, then getting them out into the open and working through them should help. If it doesn't help and/or there is no source of stress in his life, then it's solely medical (although stress will make medical problems worse). There's even an anti-depressant medicine (I don't know if it's approved for children, though) that helps some people's IBS symptoms, regardless of whether they are depressed or not. I was just reading the other day that there are a growing number of teens and pre-teens being treated for self-inflicted wounds. They get stressed and cut themselves as a way of releasing tension. Stress and depression can manifest itself in a number of ways, one of which is an upset stomach.
P.S. Sprite IS coke. Just because it doesn't contain caffeine doesn't mean it's any better for you. I always say it's the worst kind of cola because it's clear; that's just a trick to make you think it's good. It's full of sugar and empty calories and the carbonation can be very bad for people with gas/intestinal problems. If it helps settle his stomach when he's nauseated, then switch to a club soda which has the same carbonation without the sugar.
But if your son has gas problems, you really should ditch the Sprite AND the juice. Apple juice is particularly bad for most people with IBS. I can eat raw apples but the juice gives me gas, and I am one of the less sensitive people on the board. Switch him over to water. Almost no human being is allergic to water. Milk is okay in small doses if you are sure he's not lactose intolerant. If you want him to have the benefits of fruit, have him eat it cooked or raw and in small quantities. If he balks at plain water, then try herbal teas, or even kool-aid. Make it yourself and gradually lower the sugar you put into it so it's some better than colas. If he consumes a lot of fake sugars--especially sugar alcohols--cut those out. Sugar alcohols (found in anything labeled "sugar free") are bad for regular people and super bad for IBSers. And there are may people out there who can't tolerate Equal (aspartame) or Sweet N'Low (sacchrain). Splenda is still questionable because it's so new. Regular sugar in small doses, though, is better for you than any fake sugar and has less calories than high fructose corn syrup (found, I daresay, in Sprite as well as Coke).
And watch his "grease content." I found that I can tolerate the fats found in dairy, meat and oddball fruits and vegetables like avocados, olives and coconuts, but I can't handle grease well at all any more. I ate some potato chips for the first time in a few months this past weekend and woke up with it still sitting on my stomach several hours later and feeling "greasy." Anything deep fried is greasy. Anything pan fried in canola oil is greasy (although you can make it a bit better by doing as my grandmother does and blot fried chicken in paper towels). Potato chips are greasy. Most commercial crackers and cookies are greasy. Pizza is greasy, unless made from scratch. Bascially, if it has "partially hydrogenated oil" of just about any kind in it, it's greasy (soybean oil being better than canola or other vegetable oils). Don't try and get rid of everything all at once, though; try weaning him off a product (chips, for instance) once every week or two.,