Hey, I feel the same as you, except my friends are always working and so 'too busy' or 'too tired' to do anything, and then other friends always say they have no money so can't do this, or not allowed out (we're all 17). And then my brother will say how I'm a loner and I've got no mates and all the rest of it, but it's not my fault.
I've wasted the past two weeks pretty much, but tomorrow I've decided I'm gonna go look for a job, anything, even if just for the rest of summer. And if that fails, I'm gonna do some voluntary work at a nursery nearby because I wanna do early years at Uni, and so that will help me get some more experience and so get more chance of them letting me in lol. Is there anything you could volunteer for? Some schools do playscheme type things, maybe they could do with extra people? If you're gonna apply to Uni this'll look good, as it shows you give up your own time to help others. The gym could be a good idea, as I'm sure there would be lots of lads your age there and so this could be a way to gain new people in your life.
You say you changed last summer because of your GCSE's, have you done better this year because of that? If so, thats a good thing, because it means you're focusing on what you want your future to be, rather than just seeing what happens.
PM me if you wanna chat more x