Thank you for asking on HealthcareMagic.com, providing better healthcare for you. I have gone through your case and I can understand your concern. Miralax (polyethylene glycol 3350) is a laxative used to treat constipation. It increases the amount of water in the intestinal tract to stimulate bowel movements, producing a diarrhea-like effect so cramps in your upper belly and light brown to clay stools are side effects of Miralax. There s nothing to worry, because they re transitory and last only few minutes. Miralax should be used for short term relief of constipation. Get enough fluids if you use it. Hope this answers your question. If you have additional questions or follow up questions then please do not hesitate in writing to us. I will be happy to answer your questions. Wishing you good health. Please don t forget to give your valuable feedback and five star rating, to help me assist you in a better way. Click at I Find This Answer Helpful too . Please, write a review about your experience with me.