Could you get your doctor to refer you to a hospital for a different type of allergy test?
The one i had was where they put 12 drops of different chemicals on your arm, and put a small prick in the centre of each one with a blade
Some then flared up, while others stayed the same. Apparantly it flares up if histamines are released, which means you are allergic to it.
Might be worth a shot?