I’m very concerned about you. What you should do is follow the advice of the sensible part of you that got you to write to us and that knows you need some help.
I’m sure your mother means well. I suspect that she wants to think it’s a phase because she can’t stand to believe you are in tremendous pain. But what you are reporting is not usual, especially since it has gone on for so long.
Start with a visit to your physician. Sometimes symptoms like yours are due to an underlying medical condition like a thyroid disorder or vitamin deficiency. If you are medically fine, then please talk to your school counselor about how to find a therapist who specializes in teen issues.
You wrote a thoughtful letter. Bring it with you to the appointments, and it will help the doctor or counselor quickly understand your level of distress.
If you were going to get better without help, you would be seeing some improvement by now. Please take your own good advice and get the help you need and deserve.
I wish you well.