Rash/hives from drug/sun interaction. I take hydrochlorathiazide for high blood pressure and had too much sun exposure last week. I've now been itching for the past 7 days on arms, legs, and back. I've been treating with over-the-counter cortizone cream,

You . You have phototoxic dermatitis from taking hct and exposing to sun. You should wear a sunscreen when sun exposed at all times. For now you can try Benadryl (diphenhydramine) or a non-sedating antihistamine like Cetirizine and if no better see your doctor, there are other medicines that can be used to clear this. Remember to use sunscreen everytime, and apply frequently when outside.
Rash. You might need to bite the bullet and see your primary doctor to get a stronger topical medication to calm down the itch. You can also consider an over the counter non-sedating antihistamine to help calm down the itch. Ask the pharmacist to point you to this aisle.