Also a UK lad and can very much relate to the frustration of dealing with the NHS mental health service. Having read all of that I'm curios as to why your gp hasn't referred you at least to a psychiatrist as playing around with anti depressants 5 times to no effect would indicate that this is beyond his 'general practioning'... 2nd thing I found odd is that there is no mention of therapy which should be available to you (if not at your surgery, then somewhere local), ask your gp about IAPT availability... Can be frustrating in itself as sessions are slow (like once a month) but it's a start and better than nothing.

Sad reality is that in the UK you kind of have to push hard for help and when your motivation is drained through depression and low self esteem it is not an easy task... But look on the bright side, you've posted here and hopefully some of the info given above will help you take control.

TJ

Edit: just noticed Waterknobs mention of calling the crisis team. Works a bit differently in the UK (from your opening post though I think you know what I'm going to say), once they've handed you back to GP they won't help which is pretty lousy but they are over stretched or so they've told me in the past.