I have been suffering from depression. I don't feel happy anymore. What can you do to fix it?

Get help... Psychotherapy and possibly medication may be indicated. Talk to your dr. Wishing you well...
Therapy. It's important to first understand you & the issues leading to your unhappiness, before trying to "fix" anything. For most people, i believe this is a place deeper than medications can reach, and which is best accessed through talk therapy. There are some lifestyle changes that can help -- exercise, whole foods (anti-inflammatory) diet, connecting with others, etc. Antidepressants can help too.