Alright. First of all, “20″ is not old. It’s young, quite young actually. You have your whole life out in front of you.
So. On the first topic: GED and such. It is possible to finish high school/go to collage at your age. Go now, because later on, you’ll wish you had finished/gone to collage.
Second. If that’s impossible, try looking for a second job. Make it slightly better then the one you hold now. First of all, if you get fired from either, you have a fall back, and second, you can threaten one with leaving for the other. Waitressing tips (or is it waiterising tips?): be a ‘people person’. Smile tons. Ask them often if they need anything. Talk to them. People like to be talked to.
And finally. It’s ok to be lazy. I myself am remarkably lazy. But you have to struggle through it. Try eating better, sometimes that helps the lethargy. Try going for a run or such.
Good Luck.
--
I think this post is going to be coming in handy for this year. Hopefully it wont become out dated too soon.