You have suffered about this on your own for long enough! Stop thinking about going to see a professional and do it — now. It’s not getting better. It is getting worse. There is nothing to be ashamed of that you haven’t figured it out by yourself. If you could solve the problem on your own, you would have done so long ago.
There’s often a two step process to figure out symptoms like yours: Medical and Psychological. First, get yourself to your doctor immediately. There are a number of medical conditions that can cause symptoms like yours at your age.
If you are fine medically, then it’s time to go see a psychologist or other mental health counselor. Your doctor will probably have some suggestions about who might be most helpful to a teen.
I hope you have parents who can be supportive. If you haven’t told them how much you are suffering, then do. If you can’t find the words, then it might help to share the letter you wrote to me and my response. I don’t know anything about the services available in your country. Hopefully, your parents will know how to access the assessments you need. Good treatment can only happen when there’s first been a good evaluation.
I hope you care enough about yourself to seek out what you need. You need and deserve help.
I wish you well.