What's wrong with me or how do I take care of this in the meantime while waiting to see the dentist?

My best guess is just try to keep it clean (rinse with warm salty water) Sucks that you have to wait the whole weekend. I also know (having gotten my wisdom teeth out a few years ago) that part of your jaw can become exposed in the healing process. It happened to me, although it didnt swell it hurt and it was like I had basically a part of my jaw not covered with any skin. My dentist assured me that it was normal and that it might just happen time to time. In your case possibly there was exposed skin and something got underneath it (food etc) and little bacterias grew and that's what caused the puss. Although Im not sure, that's my best guess >.< Good luck over the weekend, I hope you feel better :)

Sounds like you had an absess. A course of antibiotics should clear it up. Have you been under the weather lately ?

It most definitely sounds like a relatively common condition called pericornitis. This happens when you get food packed under that flap of loose tissue behind your last tooth. Antibiotics will clear this up. If it becomes a recurring problem the tissue may have to cut back. Salt water rinses may provide some relief, it definitely won't hurt.