You sound like me when I first started. I was 14, never imagined at 23 I'd still be doing the same!

And mazing is right, it gets worse because the effects aren't the same after a while and it takes more to get what you want out of it.
I never told my parents either, but I really wish I had. If I had got the help when it first started I don't think I would be such a mess now. My parents only found out last year after a suicide attempt. They have been very supportive so all those years I spent worrying that they just wouldn't get it were pointless.
Parents are there to support but they can't help unless they know the full extent of the problem. I tried to tell my mum I was sad when I was 14 and hoped that would be enough. I missed out the fact I was self harming and suicidal though so she just took me shopping and figured that would be enough.
I know how hard it is to tell people about it though. Perhaps you could right them a note explaining it all? Would that be easier for you?