Does anyone else have this weird drug interaction?

For as long as I can remember, I have never been able to build up a tolerance to drugs. Even when I was a chronic pot smoker, one or two hits was all I needed to get really freaking high. I have been on xanax for years for anxiety, and even after taking it all this time, I only need a little bit to get the effect. It’s the same way with alcohol, and I’ve been called a lightweight because of it. Is anyone else familiar with this reaction to repeated drug use? I don’t know of anyone else that has the same problem.