my grandmother used to get shingles so bad, it was under her bra in the front, and it was so red and her skin looked like it was on fire and cracking... she went to a doctor and they gave her creams and pain killers!!
It could be a rotator cuff injury. The pain shows up between the elbow and shoulder but it usually is deferred from around the deltoid area but is really in the shoulder. I had/have a rotator cuff injury that became a frozen shoulder. Regarding Shingles, that doesn't always produce a rash. But it usually doesn't come out on the arm. You should see your doctor to confirm what it is. My injury was excruciatingly painful the first month or two and it was stabbing pain as well. The itching could just be a nerve related thing.
It is hard to say if this is shingles or not.
My advice is to make an appointment and see your doctor so that he can examine your arm and give you a correct diagnosis, or refer you for further investigation if required.
The stabbing pain could be referred pain from the spine or neck area. If you used your arm to do any heavy physical task that could have done some damage, but that would not make it itch.
With the itching, have you been near anything that could have triggered this off, stung, bitten or scratched? (Just something to think about).
If the skin does hurts to touch (accompanied by the itch) it may be an infection.
Make an appointment to see your doctor so that you can get the correct diagnosis and the correct treatment.
Let me know how you get on.
Best wishes.