Flip Your Mindset
Let me share with you what worked for me. Instead of believing that others (most, anyhow) were happy while I was not, making me feel lost and filled with woe, I decided to I believe we were put here in order to suffer—and withstand it. If you give up, you lose. What is the penalty? Not a clue, but I sure and s*!# don't want to find out! This also means all the "happy" people I frankly did not see eye-to-eye with or couldn't be bothered with me will win. Why should they win? They are no better than me, maybe blind to all of the evils or sorrows, but certainly not better, because I feel deeper and I care more. My pain beats their superficial cheerfulness.
This might sound strange, but in the hardest times emotionally and mentally, you have to be willing to try something a little weird when all else fails. Change your thought processes. Allow yourself to be angry if that works. Or competitive, such as I did.
I wish you all the best and sincerely hope that you find what you're looking for.