Ugh, we dealt with this for the first 5 years with ds. We'd clean him out, he'd be fine. Then his eating would decrease, stomach would be distended, sometimes he'd vomit... Vicious cycle. We found with him though because his eating REALLY decreased -- a chicken nugget would make him full --- and he'd vomit if he ate more that his was caused by adhesions from his original surgery narrowing a portion of his intestine so his enzymes weren't getting where they were supposed to get to. So his issues were mechanical in nature once they figured it out.
That said, his digestive system for the most part is pretty normal; however, if he gets a stomach bug -- we deal with motility issues for days if not weeks. And if I don't limit his peanut, nut intake to just a couple small portions a day, he'll get plugged up and it's time to break out the milk of mag.
Might be time to have a gi scan or motility study done. Although having a tween girl I can't imagine how a gastropgraphin (sp) enema would go over. Or it might be time to switch it up to golytley or oral mucomyst. I know a couple people who take mucomyst orally to clear out the gunk -- usually mixed with coke or juice to mask the aroma.
