I used to have this problem because my diet was too acidic--that is metabolized as acidic. Ironically the most alkalinizing thing is lemons. Can you get some fresh lemons and agave syrup or xylitol at a health food store, if you can't then brown rice syrup or raw honey. The lemons are very alkalinizing and these are alkalinizing sweetners. Give him the lemonade on a regular basis. DO NOT COOK THE LEMONS OR GET BOTTLED (PASTERIZED AND COODED LEMONS)! They must be fresh squeezed from the lemon!
Is he drinking sodas, iced tea. Is he not eating plenty of vegetables and salad?
Other alkalinizing foods are watermelon, papya, almonds, raw almond butter, most fruits (except blueberries and prunes). All greens are good and vegetables, avocado. Yogurt is neutral. You can find lists on line to find your favorite foods and whether they're alkaliniziing of acidifying.
Of course, like other people are saying, it could be anything, but an alkalinizing diet is good for everyone's health.
_________________
"Me voici donc seul sur la terre, n'ayant plus de frère de prochain d'ami de société que moi-même." Jean-Jacques Rousseau
"Do not think, 'I am alone.'" Sasaki Roshi
WonderWoman