Hmmm well as far as A-Levels go, what are you interested in and what do you reckon you might like to pursue as a potential field of employment? (I'm saying this to you while still working out what I want to do myself but anyway
). As for where you go to do them, I'm not sure
Making friends. Well whatever A-Levels you do, you're bound to meet someone in your classes whom you might have stuff in common with and get talking to and make friends with.
Changing diet is a gradual thing (I could do with changing my diet really :P). Just gradually alter your diet until you get into eating better? Exercise...maybe join a Gym or something?
Tiredness. Do something in the day to make you tired, then you'll go to bed and fall asleep quickly. You should in theory of had a good nights sleep. Get up early the next morning and try and do something to make you tired or whatever again... Break the cycle of sleeping in
(again I'm telling you this, but I'm guilty of sleeping in and I really should change this :P).
Happiness...that's a tough one and I'm still looking for the answer myself *sigh*.
Make more friends. Go out and socialise or join something you're interested in
(once again, giving you advice, but I'm pretty much in your situation myself here...).
Less anxiety. Another hard one that I'm also experiencing. Have you ever thought about meditation?
I hope this was of some help haha
Dunno if it was really or what