I never actually understood why the need to pursue constant happiness. It is as fleeting as sadness. The trick is to be content. Manage what is within your control and let go of what isn't in your control.
And I've never understood why some people think "JuSt Be CoNtEnT" is a sane response to someone saying they're unhappy. In your experience, how often does saying that actually help someone?
The media had ingrained us to pursue happiness, and everything will be fine. We will all get "good ending". But movies never tells us life goes on. Anything and everything could happen-- happy or good. The reality is that the universe is indifferent and it is what it is. From my experience, many people's unhappiness comes from not accepting the situation as it is, and holding on to their view of what the world should be in spite of what reality presents.
It takes a long time, but learning to know when and where to use emotions is important. This is not a slight to anyone who are feeling down, but in my experience many people also place too much value on certain things that do not matter in the grand scheme of things. Be it status, others' opinion, material wealth, rejection by a crush, etc. That's not to say that one should not pursue more earnings and live like a pauper, or "just get over" a crush rejecting you, but you could control how you react to them, not the circumstances controlling you. There are many other potential singles out there you could ask out. It's perfectly fine to buy an expensive item if it makes you happy, but what good is a $300 vase for showing off if you have nothing left to buy food? And if that vase breaks, why be upset over a broken vase which does not fulfill any basic necessities to survive? And if you did something embarrassing in front a stranger in a park, why mind the opinion of a person whom you will most likely never meet again? We all stress needlessly and that is a challenge we all have to overcome.
Talk to your doctor about depression. Otherwise maybe try shrooms? If your comfortable with the idea have a friend to guide you. (They're antidepressants similar to SSRIs)