First of all, cheer up - these aren't actually the best days of your life like many people will tell you but they are pretty damn close, especially if you stop over analysing everything and worrying about what you should be doing with your life. Yes,there is more to life than working on a checkout but don't worry about it, it will work itself out eventually for now just go with the flow.
So, you haven't got a boyfriend, get over it. You don't need one and seriously have you seen the guys you hang around with anyway? Someone will tell you that boyfriends are a bit pointless at this age, you will think this makes no sense but they are right!
Just so you know, a 'date' does not mean a relationship will follow, but don't worry about that either - just have fun ;)
Try and stay in a job for more than 6 months, they will all be fairly crap but keep changing them won't help you, the next one will be just as bad and it will just make writing your CV a pain in the bum. You won't be there forever and one day they won't seem anywhere near as bad as you thought they were, ad you might even miss those days (but only a little bit!)
Don't spend too much money, (and yes annoyingly I do sound like your Mum) and don't get a credit card, or when you do stop increasing the limit. This will be a disaster and when you are lucky enough to get back on your feet don't bloody do it again... twice!
Finally, and this is important....
You are not as fat as you think you are - yet!
Stop eating so much crap and learn to cook something other than cake but when you don't bother to do that and suddenly realise you cannot buy anything to fit you then don't sulk about it for years. Realise you are NOT big boned, and get off your backside and do something about it. You CAN (and will) be a size 12 if you work at it.
But most of all have fun, everything is not as bad as you think it is and stop expecting the worst to happen 'so you are not disappointed'
Love your older, slightly wiser and certainly more boring self.
P.S. When you pass your driving test.... DRIVE CAREFULLY!
Linking up to Flashback Friday