Hello! Thank you for the query. Your symptoms can be a side effect of chronic Miralax use. Laxatives medicines should be used only temporarily, otherwise diarrhea, stomach aches, strange noises can appear. Thyroid disease and improper thyroid hormones level can cause constipation (in case of hypothyroid) and diarrhea (hyperthyroid). Other possible reasons of constipation are medicines (ca-blockers, antidepressants), chronic bowels infection, partial bowels obstruction due to inflammatory bowels disease. Rash on the arms and legs (and joints pains) can be a symptom of inflammatory bowels disease like Crohns disease. So if you can not find the reason of your digestive tract problems, this should be considered. I suggest you to check your thyroid hormones, have stool tests, blood work. Colonoscopy and abdominal CT with oral contrast should be also considered. Hope this will help. Regards.