Don't know how accessible or affordable therapy is where you live, but you certainly need someone to talk to.
I had a midlife crisis in my 40's. My career was going nowhere, I was trapped in a job I hated. I felt I was wasting my life.
What kept me going was the sense of obligation I had to others who depend on me. If you have nothing or no one to whom you owe service, then you can change that. Find a partner, or volunteer yourself for charitable work. By helping others, you also help yourself.
I made a point of enjoying the little things in life. Exercise. Walk in the sun. Go fishing. Grow tomatoes. Buy a friend a drink. Whatever, just sneak the little pleasures when you can.
I set some goals. Not boring goals like to make money, goals to achieve something meaningful, that engaged my interests and (modest) abilities.
Things got better. My 50's and 60's were some of the most rewarding years of my life. (I'm 69 now). I achieved some things I'd never thought I could achieve, just by pluggin' away.
Life is hard. John Stuart Mill wrote that most people have a limited capacity for happiness. I think that is true. But the strange thing is that by relieving yourself of the obligation to feel happy, sometimes it happens anyway.