I don't know how it works in England, but in the US schools are required to have a school counselor. If yours doesn't have one, try asking your GP. He can point you in the right direction. Again, I'm sorry I'm not familiar with how things work over there, but here a person has the same rights with mental health as physical. They can't tell your parents unless you're in danger of hurting yourself or someone else.
BeenThere is right... 16 is a difficult age. You're going through so many changes and it's normal to feel messed up. I don't know if there's anything going on with you on top of that. A good rule of thumb is that if it's interfering in your life, that's when it's time to start looking for help. Sounds like that's where you are.
I would guess that your family would want to know you're in pain. I'm sure they love you and want you to get help.
If you want to talk, you can reach me in PM or on msn. I'm here for you hun.