You ask, “How can I be happy if I am not?”
True, you can’t control the way you feel, but you do have control over your conscious thought, speech and actions.
Do something simple: Think good thoughts, speak good things, behave the way a joyful person behaves—even if you don’t fully feel it inside. Eventually, the inner joy of the soul will break through.

Control over our conscious thought (as well as speech and action) does provide us control over how we feel.
An example of I control how I feel: if someone pats my knee at an unwanted time, I feel fear/anger, while if someone pats my knee to say “good job”, I feel happy/proud. Same stimulus, but totally opposite feeling. I control that.