Red, raised, itchy rash

I did have that once, about 20 or so years ago. I don't know what it was, never found out. I have a feeling it may have been some sort of inflammatory response as I later discovered I had an undiagnosed auto-immune condition I'd probably had all my life. I had quite a bit of stress at the time.

Sounds like hives (or urticaria, medical term).
I have been dealing with this menace for 5 years, it began a day after the Pfeiser covid booster. Not saying that's what caused yours but just for context I know what it feels like.
Aloe Vera gel (kept in the fridge) helps a bit. And Cetrazine seems to be the best anti histamine, recommended by G.P.

There are multiple things it could be, as well as multiple things that can have set it off.
I think you will need to contact a GP.

Try asking your pharmacist.

Could it be caused by something you have handled in the garden? I get a similar rash when cutting down ivy if it touches a part of skin not covered by clothing.

I had a rash like that when I was in my 30's ,it started on my back then spread to my chest , elbows to wrist and thighs to knees, it looked as if I had been stung by nettles, it was extremely itchy, GP sent me to see a skin specialist,but as usual by the time a got to see the specialist it was almost gone...3 months it lasted.
He told me it was PITYRIASIS ROSEA and once I'd had it , it wouldn't come back...and it hasn't .

I had a similar rash a few years ago on my face and upper body. Very itchy and tingly.
The culprit was a new shampoo I was trying. It had tea tree oil as part of the ingredients. I stopped using it and the rash went.
Have you changed to a different shampoo recently?

No, I haven’t changed any toiletries. I only use soap in the shower (not on the rash) and a mild shampoo once a week. I don’t wear perfume and very rarely use make up. Thank you for your comment though because it may help someone else.

It maybe quicker to see your local Pharmacist.