Hi, welcome to HCM, Stomach ache and fever are common side effects, and that we can control by giving Allopurinol in small and gradually increasing doses. If urine and stool are showing blood you should immediately report this to your Doctor. Allopurinol is very good medicine to reduce uric Acid level in blood, but if you have these side effects, your Doctor has to choose other options. I hope your Doctor has given you handouts showing the foods and other things to avoid to reduce the recurring Attacks. You must avoid dehydration, so do not take Diuretics, Alcohol. You must avoid all high purine content diet, low fat, high fiber diet, and diet rich in Potassium. You must drink fresh lemon juice after each meal. Half tea spoon of baking soda with meals also prevent gout attack. Febuxostat Oxypurinol and vitamin c are other alternative to Allopurinol . I would advise you to immediately consult your doctor.