I just started a thread about the same sounding rash from a plant I do not know what it was. It looked like an vining umbrella plant.
Any how I bought the dollar store brand of hydrocortisone 1% cream and their brand of allergy medicine with antihistamine. It has helped but I read here about banana peel so I used it in the few bubbles I have on my face. WOW the peel worked GREAT it's drying it up already and the itch is gone!!
I'm going to try it on my arms when the itch comes back. It's a good thing I bought 8 bananas today. Banana peel is the way to go.