Depressive personality

For years I've felt down to such a point where I can randomly get angry, feel worthless, feel like I can't live any longer (not suicidal thoughts as such but lacking the will to live). I can never get a good nights sleep, I always wake up tired and exhausted. I can never concentrate or focus on anything and my university work and knowledge has plummeted.

I have friends who are on treatment for depression and said they were classic signs so I decided to take a trip to my GP. Basically he said it was just my personality and wouldn't even think of drugs as I am only 20 and doesn't want me to develop a resistance early, or some other bogus reason.

What I'm confused about is how this can all be caused by my personality. I had a "bad" childhood to put it lightly but seemed to be cheerful until around the age of 14-15 when I couldn't do my coursework, think straight and started to feel generally crap all of the time.

Could anyone shed any light on this as I doubt it could be a personality thing. Might consider getting a second opinion from another doctor at my local surgery.

Thanks in advance.

[capegirlnoshoes]

DEFINITELY go to another doctor.  20 is DEFINITELY not too young to be on anti-depressants, and it's physically impossible to 'build up a tolerance' to them in the way you're talking about!  Trust me, I have read studies on them!  And am on or have been on several psychiatric drugs, and I'm 19!  
Telling you it's just your personality is rubbish.  There is no such condition as Depressive Personality Disorder.  I have the Diagnostic and Statistical Manual of Mental Disorders right here with me now.  By definition, if something is bad enough to really interfere with your functioning - as this evidently is - and it's not going away anytime soon, then it is a disorder.  
Your GP also plainly knows nothing about the pattern of onset of more serious psychiatric disorders (which is common among GPs, sadly).  Both schizophrenia and bipolar are often preceded by a 'prodrome' period in which depressive symptoms can feature very prominently.  Which is not to scare you by saying you have schizophrenia or something like that because like as not you don't, but you might!  So problems like yours shouldn't be just chucked out as 'personality' without careful screening and even monitoring.