- Life exists because the environment allowed it to exist. It has no purpose or divine right to feel good.
- Living organisms, including humans, are built to survive, not primarily to be happy
- Happiness is part of the human condition, but some people will find it more difficult than others to maintain inner wellbeing
- There is no divine force willing you to be happy. Only you and maybe other conscious beings that know of your existence care about your wellbeing because it's part of their nature. All you can do is increase your chances of being happy through effort.
- In relation to point 4, you're going to have to bring acceptance to this and acceptance to how you feel, rather than resisting it, but one thing that might help is realising those "happy" people who you are angry at may not be as happy as you think.
- Accept the hand you've been dealt, and just do your best with it
- Don't compare your life to anyone elses, it will just make you worse, which is self-evident with the way you're feeling now.
This is all true, but most likely not new information to anyone here.
How to actually change your train of thought is the million dollar question, one with no shortage of theories.
I assume OP is venting and not seeking these theories, though I would second that anger makes things worse; I am happy for the people who are [seemingly] happy, I just wish I and everyone who feels the same didn't have to be part of their [seemingly] happy world.