I hate that I don't have happiness and positivity even tho I tell myself to. Why doesn't this work?

Happiness comes from being contented. If there are things that keep you discounted, money troubles, a job you dislike, family who are verbally abusive, a partner who doesn't appreciate you, kids who are out of control happiness could be just around the corner, but this one thing keeps it from coming to you.

Don't look for the happiness. Try instead to figure out what's the biggest negative factor in your life that's making you discontented. And work on changing that.