The back of my legs itch bad. when i shave it goes away. when the hair grows back it itches bad. i've had it for some time and doctors have given me antihistamines for it. one doctor said i had an allergy to my own hair.

Itch: I don't believe that you're allergic to your own hair. Itchiness without a rash can be caused by dryness,reaction to clothing,soap,creams,etc especially if you notice itchiness elsewhere in your body. I think you'll have to experiment and try to pinpoint the cause.

Irritation?: Your hair is likely very curve and thus when they are long enough they may start to "tickle" or irritate your leg. This would not be helped by taking an antihistamine although a topical numbing agent or cortisone may. Since you have already found the solution, why not shave more frequently?