I have dark spots, red patches, itchy painful skin rash. The hospital said it was a allergic reaction but couldn't figure out what caused it.

Allergic rash. See your dermatologist for evaluation and treatment of your rash. There are treatments that will work even if you don't know the cause of the rash. It will be important to be sure it is not a reaction to a medication. Allergic reactions can come from inside the body or from external contact agents. If your dermatologist suspects an external contact agent they can perform patch tests to look for.