This is the first post that has struck on the answer that I have come up with after suffering for about 10 years with these symptoms.  Seen lots of doctors and none of them ever found a cause or a cure.  Oddly, whenever I had symptoms of a yeast infection or bacterial vaginal infection the bumps would occur.  Starting in the legs, mostly inner thighs, inside of shins, back of the knees, inner arms from wrist to above the elbows.  Made worse by scratching, for sure!  Starts off with a "prickling" feeling to the skin, especially while bathing, then the itching starts.  I found on my own that if I treat myself for vaginal yeast infection and take a high-powered allergy medicine (doxepin), the bumps go away in a few days.  I have a tendency toward recurring yeast/bacterial infections, so I maintain health in that area by alternating treatments of iodine douches followed by yogurt for severe symptoms, or "Yeast Arrest" suppositories for several days as a treatment for mild symptoms or as a preventative.  My ph is too alkaline to support healthy vaginal flora, so I do this regularly and it keeps the rash away for months and months. Needless to say, ask a doctor in case you have a special situation and before using iodine or any other product on yourself.   Naturally, a healthy diet and preventative measures such as are necessary to maintain a healthy ph level would help tremendously.