Emotions are contagious. Ever been around someone in a dark mood? Hard not to be brought down. if you aren't careful you might start mimicking their behavior. As is with happiness, it's contagious, you start spreading it first with smiles.
Ecclesiastes 3:12 "i know that there is nothing better for people than to be happy and do good while they live." Gods not talking about the fake "i'm gonna act happy" smile. But from your heart. And as the verse says we need to "do good" while we live. Small examples are, . . .if the lady next to you needs help grabbing an item on the shelf, help her, don't just pretend she's not there, or you don't see her. Or a mentally handicapped person is at the store, and everybody there is avoiding eye contact. Say hello! Smile! You know how many people ignore them.
Psalms 68:3 "But may the righteous be glad and rejoice before God; may they be happy and joyful." My prayer is that you find your joy. God can give you a peace that is beyond human understanding, and he can help lead you to joy in Him. Psalms 66:1 "Shout for joy to God, all the earth."