The amoxicillin is an antibiotic and belongs to class of antibiotics called penicillins. It can be used if refrigerated at 20-30 degree centigrade but can can not be used if frozen because the frozen amoxicillin looses its stability between 0-20 degree centigrade. For your confidence, read this study.
Never used mixed then frozen
Check the label as it usually has a discard date on it.♥ If not passed date thaw & enjoy....LOL!