I realized that I have never tried to figure out how much sleep I need. From reading a few articles on the web (wikihow and WebMD), it seems like I should first need to normalize my sleep schedule (go to sleep and wake up at the same time every day for 1-2 weeks). Then I should sleep in on a weekend and see how long I naturally sleep. If it's longer than my regular sleep schedule, then I know I need to sleep longer. If it's shorter, than I know I'm getting too much sleep.
I don't know when I'll be able to do my sleep experiment. But the sooner I figure it out, the better.