Hi & Welcome. I appreciate your concern for your beloved husband. Inadequate dose of Amoxicillin, any other medication taken, age ?? The antibiotic Amoxicillin is commonly prescribed to treat susceptible bacterial infections like sinusitis is generally safe however its most common side effects can include: allergic reactions, nausea, vomiting, diarrhea, and rash. It is unlikely to cause hematuria (blood in the urine). He needs to be examined in ER to rule out stones, inflammation or infection of the urinary tract (kidneys, ureter or urinary bladder). Hope this will help him. Best regards.