hopinso
Try boiling some whole flax seed in water for a few minutes, then allow to cool. The water will turn quite thick. Strain out the flax seeds and stir a tablespoon or so of this flax seed mucus into juice a couple of times a day. This will lubricate the intestinal track and make bowel movements easier and faster. It is not a stimulant or a fiber, just a lubricant. The mucus is tasteless, but very gross looking and has a strange texture by itself; however it is undetectable in juice. You can also stir it into yogurt or smoothies. It should be fine to increase his magnesium to 1000 mg. Magnesium oxide is not easily absorbed, so the chances of him getting too much magnesium is minimal.
Having a stomach ache may indicate he is not clearing his bowel, or he might have a small stricture that slow downs the normal movement and causes pain when the stool backs up and is not released. Liquid stools may help relief this problem.
Make sure the boy is drinking plenty of pure water and is not eating much in the way of sugar, grains or dairy, all can cause inflammation and mucus.