Bonnie,
Is your son constipated? I'm assuming he is if he's on a laxative. You might look into the subject of "friendly-bacteria" or "probiotics" and also lacto-fermented foods (i. e. real yogurt, kefir, raw sauerkraut), which might help.
A lot of people in our society have little or no lacto-fermented foods in their diet, and as a result may suffer from a variety of digestive disorders. To make matters worse, antibiotics kill off not only most of the harmful bacteria, but the beneficial bacteria as well, which can allow harmful organisms to take over the digestive tract.
In addition to lacto-fermented foods, there a variety of "probiotic" supplements on the market .
The potential benefits of probiotic supplementation and the consumption of lacto-fermented/cultured foods in the diet may include:
1) beneficial effects on immune function
2) possible protection against pathogens by competing for nutrients and attatchment sites in GI tract
3) decreased incidence of respiratory tract infections
4) decreased incidence of dental cavities in children
5) the treatment and prevention of acute and antibiotic- associated diarrhea
6) decreasing the severity and duration of rotavirus infections in children and travelers' diarrhea in adults
7) eliminating milk allergies and decrease the risk of atopic aczema in children.
8) correction of poor absorption of trace minerals, which may occur in people whose diets are high in mineral-blocking phytic acid contained in soy foods, whole grains, nuts and legumes.
9) improve bowel habits and reduce incidence of constipation
That's just an idea of what probiotics/lacto-fermented foods can help with. Hope this helps. But you might want to have your son checked out for other possibile health problems