@msolga,
We all deal with such things throughout our lives. It's easy to generalize about remedies, but hard to really connect with other people regarding them. However, I'll try - even though I apply them only imperfectly in my own life.
To a large extent happiness is a choice. There is always reason to be sad and depressed: life ends in decay and death; things go wrong all the time; and hopes are not always fully realized. However, there are also almost always things to be treasured and reasons to be joyful. Choose to connect with the good things about you; the people you meet. Choose to be happy for them.
Try to connect with the people you encounter and see things, as well as you can, through their perspective. Find (or try to find) something you like in everyone. Be persistent, because it doesn't always work at first (with some, alas, it doesn't work at all). The effort gets you out of what may be a depressing cycle of self preoccupations.
Physical exercise and activity is indeed important - our nature requires it. Regular hard physical exercise was part of the routine at the Naval Academy and in Flight Training, and it became a habit that has stayed with me ever since. Hard exercise doesn't solve any of my problems, but for about twenty hours afterwards, I don't give a damn - then its almost time to do it again. It also makes it easier for me to make the wise choices indicated above. (I'll confess that I often have to force myself to do it - the wise understanding often comes only after the workout
).
Don't become preoccupied with the many imperfections of the world and human society. The planet we inhabit is and has always been an unstable and dynamic thing - mass extinctions, geological and climactic changes are the rule, not the exception. One day the expanding red giant sun will engulf it all in a fiery end. Humans (and other creatures) have been killing and exploiting each other for as long as history records events. All things considered, we are doing it relatively less now and our species is thriving. Our lives and our environment are fleeting things whose end is knowable, even if the origins of our existence are not. Still, it is a hell of a ride !
