I am moved by what you say Serkeen - and hope that what you've read from others here has helped. My own thoughts are , that our lives are both light and shade, but it is easy nowadays to believe we 'should' be happy much of the time. There is no 'should' about it, and we do experience happy as well as sad feelings; trying to somehow get rid of feelings doesn't seem to work. But we can look with awareness , though not with judgement of good or bad, at our thoughts , and ask ourselves if they are true. Our thoughts seem to us to be how the world is, but actually many of them are not the truth when we look at them with a willingness to challenge them and be open and honest. Letting go unhelpful and untrue thoughts can help more than you may at the moment believe, but be ready to relax and smile when the old thoughts come back. Resist blaming yourself when that happens; it takes time to change habit patterns in our brains and minds, and feelings follow our thoughts.
Many people feel happier if they walk most or many days of the week - for half an hour or preferably a bit longer, and some of it to be brisk. Walking helps lift our mood and we evolved to be out of doors under the sky - walking works well for our brains as well as bodies.
People also often feel better if they do volunteer work for others - but if you do, it is not helpful to be driven too strongly by the wish to be good, but to do it with an open heart.
You may find this book interesting and helpful: do not be put off by its odd title! It is Counselling for Toads by Robert de Board. The Toad in the title, is Toad of Toad Hall, from the The Wind in the Willows, and it is easy to read. If you've not read The Wind in the Willows, it doesn't really matter. It helps understand what goes on in our thoughts and what we can do to be freer and more fully ourselves. There are other books I find very helpful too, including a fairly new one called The Power of Meaning by Emily Esfahazi (I may have got this bit of her name wrong) Smith.
Serkeen, along with so many others I wish you well.