Do you have specific goals to go towards? Reexamine them and see if you're still motivated towards them. Alternatively, set a bunch of new goals you're not sure you really want and just go after them. I'm finding a derth of goals I actually want, so I'm going after a bunch of other stuff to work on my self-discipline and determination.
If you don't already, create a daily checklist of stuff you'd like to do. Like, set quotas for stuff, like do x for an hour or somin. and then keep track of it.
Reread Pavlina's old blogs, before about june 05. I'm finding that I just need a little reinforcement to keep doing stuff, which I used to get from Pavlina but now he's talking about IM a lot more, which reinforces that but weakens my productivity. I actually just wrote about this on my blog:
Insanity Studios Inc.
Alternatively, you could block those websites for a certain period of time, either by removing any links (so you don't impulse-click them) or creating a new profile on your computer called Work ro whatever.
You said you'll be startin college soon? Maybe start making some goals to improve your academics. Pick up some books on getting good grades, or something.
Write five ways to imrpove every day for a month. At the end you'll have 150 ideas, some fo them have to be useful.
There's a bunch of ideas, some low level solutions, so higher level. Good luck and I hope this helps!