The teenage years are so difficult for most anybody, and when you are suffering with something more, it makes it doubly difficult. I know that you mentioned that you were too shy to talk to somebody about this...and asking for help is the hardest step to take. But, it will make things easier in the long run. You don't have to suffer through this silently, there are people out there that can help you. Try talking to your doctor and/or a school social worker. That is what they are there for, to help you. Remember, you have to take the first step...it won't just fall into your lap.
You deserve to be happy, so please seek help. It is a long road to recovery as well, if it is depression that you might be diagnosed with, but there is hope for recovery. Don't give up, and please take that first step soon.
Will be rooting for you!