I always thought I was an introvert, but I never had this energy problem people are talking about after being social for a long period of time.

My problem was that I just couldn't get outside my comfort zone. After years of forcing myself outside my comfort zone (which many people don't or can't do), I don't really have a problem anymore.

One of the problems with being introverted is that you will probably get passed up for promotions at most companies. you need to be social to move up the ladder, even if you are a developer.