OP, here's the thing: life IS suffering.
There is no escaping that.
Birth is suffering. You do not ask to be born, being born means you WILL experience extreme suffering. That is the case for all living things. Even if you live a life of pleasure, richness and have everything you could ever ask for, eventually you will die, and all of that will be taken away. This is not pessimism, this is fact. No one, no matter how rich, has managed to escape death, and in our lifetime, no one ever will.
Outside of death, there are many other ways to suffer. To want something and not get it is suffering. Be it money, fame, a lover, a better face, a better mind, a better body. To want these things and not get this is suffering. To spend time with people you hate is suffering. To lose your loved ones to distance, old age, or a falling out is suffering.
Life is suffering, my friend.
Happiness is fleeting, for even at the most happy you will EVER be in your life, it will only last a moment. Then it will dissipate like a puff of smoke, and you will grasp at it trying to keep hold of it as long as you can, but, just like smoke, the more you flail and try to keep it nearby, the more swiftly it will disperse.
We all have to realise that happiness is unattainable, and life is not about being happy anyway. Life is about showing compassion for those around you. Be it your mother, your father, your dog, or a homeless person on the street. Showing compassion to others, and being kind, and virtuous in your everyday life is the only way to maintain some kind of mental stability.
It is not happiness you should seek if you want to feel better. No, the only way to lift the heavy burden off your soul is to give to others. Give them your time, your energy. Give them your love and your understanding. Give them your food, and your money. Give until you think you have nothing left to give and I promise you will feel lighter, calm, and stable.