Red rash under the skin with constant itching

Our 9 year old daughter is experiencing what looks like a rash, but it is under her skin.  It's a blotchy, redness that spreads on her forearms, chest and back.  A few weeks after her first incident, her sister was diagnosed with Fifth Disease and recently got over it.  That made us wonder if this was what our 9YO was experiencing.  Unfortunately, she is experiencing this itching again.  

There aren't any outbreaks above the skin that would cause scabbing.  We have tried children's Zyrtec or Claritin and neither has brought relief.  We've also tried baths and lotions.

Does this sound familiar to anyone? Please help.  I am desperate!

[Dr_Aparna]

Hi,
Looks like she has developed an allergic re-action.

Hives are red, itchy welts or swellings on the skin that often come in clusters. They
look like large red circles. In doctor speak, hives are known as "urticaria."
Hives can appear anywhere on the body, cropping up either in one small area or covering large patches of skin. They most often occur as part of an allergic reaction. No one lesion lasts more than 24 hours, but new ones may continue to appear until the condition resolves.
Although hives can be highly uncomfortable to have, they are relatively harmless. Hives usually appear suddenly and go away on their own in a matter of days, hours, or even minutes. Chronic hives, however, can last for six weeks or more.
Hives are often caused by a hypersensitivity to:
•Foods (commonly eggs, shellfish, nuts, berries, dyes, or other additives)
•Drugs (any drug can touch off an allergic reaction, although allergies to penicillin, sulfa, and aspirin are especially common)
•Pollens and plants (nettles, poison ivy, poison oak, and so on)
•Animal fur
•Insect bites or stings
•Exposure to heat, cold, or sunshine
In young children, a viral infection like a cold may trigger a bout of hives. Other potential triggers include physical exertion or exercise, stress, illness, chemicals, cosmetics, textiles, and pressure from materials rubbing against the skin.
soothe itchy skin, try cold compresses, calamine lotion, a cool shower, or a tepid bath with a few tablespoons of cornstarch (the kind sold in drugstores) thrown in.
You could give her Benadryl for the itching.
ref:http://www.myonlinewellness.com/topic/hivestreatment