Thank you for writing. At 15, it is too much to expect of yourself to handle the intensity of such feelings on your own. Feeling like you want to kill yourself is not something to ever take lightly.
The first stop should be with your doctor. These symptoms started with the onset of puberty. It may be that the problem is hormonal.
If you are medically fine, then I do suggest an evaluation by a mental health counselor.
Early diagnosis and early treatment is always a good idea. Otherwise, you will be dealing with both the original problem and the stress build up that has come from trying to manage it on your own.
Please show my response to your letter to your folks. Whether or not they believe you, the conservative thing to do is make those appointments. They have nothing to lose except a copayment or two. That’s much much better than losing the child they love because something serious went untreated.
I wish you well.