Thank you M. for your interesting question.
I see that you have taken a lot of steps to try to deal with the problem. That is assuming that it is a problem in the first place. Because some people just are born sad and most people do not know their "purpose" in life until much later in their lives. Comparing ourselves with other people causes a lot of our suffering.
Reading about something and understanding it is absolutely different from doing it. You should see a psychologist for long term therapy.
Take care and hope that you find some hope.
