It could be hives, an allergic reaction, or any number of things. It's best to call a dermatologist immediately.
scabies
Sounds like ringworm
If you are itchy on your arms and neck it may be allergies. The only way to know for certain is to see a physician.
skelytal system
Approx 1.5
Your arms
Yes, I have personally experienced this one.
You will have large spreading sweat stains under your arms.
your arms?
Yes
scabies
The red itchy spots can be many different things. It could be some type of allergic reaction. It could also be poison ivy.