If you are only using Alprazolam (Xanax) every week or two, you most likely haven't developed any kind of tolerance at all. This is excluding what you might call "subjective tolerance", that is, you're more accustomed to the drug's effects, so they don't feel as intense or powerful.
When I was sixteen, 2-3 drinks would be enough for me to go to a party and socialize. It seemed to be powerful enough and loosened me up as I wanted it to. Fast forward to present day, I don't ever drink Alcohol, but if I did want to for the same purposes as I've stated, I would probably take 6-8 drinks in an evening. I'm sure there's a physiological variable at play, but for the most part, the drinks just don't "seem" as powerful. Basically, you want to familiarize yourself with the difference between subjective and objective tolerance.