The false beliefs, opinions, impressions, and ideas that you carry in your mindset are the source of your unhappiness. They not only distort your perception of yourself and the world around you; they also conflict with each other, thus negating some of your creative energy (which, in a happy person, “flows” freely).
These things in their entirety form what you might call a false self, which you might incorrectly identify as your True Self.
You can increase your level of happiness by 1) identifying the false beliefs, attitudes, and so on and 2) deleting their effect on your present life by recognizing when they entered your experience (likely when you were a child or youth).
A good way to do this is to learn a good self-hypnosis technique and learn to follow the path of a present problem or false idea backward (through similar events in your past where the same problem appeared) to the original event.
Meditation can be useful to achieve this mental state, too—whatever you do to put your body at rest, while maintaining conscious mental focus.
You will find your level of happiness increasing each time that you identify and do away with a present problem. You will also feel more “enlightened” with each jump in happiness. Your True Self is naturally happy, and it’s who you really are when you remove the trash you’ve collected in your mind—trash which obscures your view of yourself and life.