Hugs Cate64 I feel your pain my skin is my reactor to things....
It is hard when we don't believe we are being listened too...
I wish it was as simple as just having a bath in something to get rid of it...
It is OK to VENT on here we get you ....
Can you try some Epsom salts to soak your arm in it tepid water plus Epsom salts maybe lather on some moisturizer or coconut oil after to see if that helps you with the itch and heat.
I soak in cup of Epsom salts in bath for 20 mins it helps me settle my skin but I know we are all different.
I hear you more hugs
Solidercrab