I have searched and searched and this is the only thing that I found that dealt with itching...particularly after a bath!
DERMOGRAPHISM: this can appear at any age, but is most common in young adults. The onset is usually gradual, but can also develop in a matter of days. Attacks of itching can sometimes have weals from scratching and the symptoms are worse in hot conditions...ESPECIALLY AFTER WARM BATHS!!
Minor pressure from clothing, chair seats, etc. can start up the itching and weals (as well as towelling after a bath). This condition can occur with "Mechanical hives" (uticaria) and can last for month or go on indefinitely.
It is suggested that you consult a dermatologist. In the meantime, use antihistanines. Avoid HOT baths or showers and rough toweling.
Also, it suggested that stress and connective tissue disorders (such as LUPUS) can bring on an onset (as well as allergies, infections and some medications like quinine such as plaquenil and other anti-inflammatory drugs). The chronic condition of this illness is usually due to an autoimmune disease such as Lupus where the body is allergic to itself!
Your dermatologist may be the best person to speak with who will work with your rheumatologist to determine exactly what is going on and what your treatment should be!!
I hope that I have been helpful!
Let me know what you find out!