Why Doesn't The Lidocaine At This Doc's Office Work?

I would ask them to possibly draw it up from the bottle while you are there so you know it hasn't been sitting around too long. It is supposed to last up to 7 days in a syringe but most people don't hang on to theirs that long. It does work instantly but if you give it a little longer to diffuse (like 1-2 minutes) maybe it'll work better on you. I have a few patients for whom I just have to put a little more than normal in, and I have to wait a couple of minutes. All my other patients do fine with the procedure right away.  You don't want to wait too long (like an hour) on the other hand, or you may metabolize the lidocaine if you are a fast metabolizer. 

You are correct - allergies to sulfa drugs have no bearing on the effects of lidocaine. Even expiring lidocaine should be more effective than what you are describing. I think it's time for you to find another dermatologist!