What makes you feel happy ? ( Please help me correct this notebook below, thanks in advance )

When I was about 15 to 18 years old, I felt happy and satisfied with everything I got. At that time, I found my life was very simple and full happiness. After entering the university, my positive thought almost disappeared. Instead of being sadness, depression. Through 4 years in university, like young people others I was always suspisious my ability. I regretted what's gone and thought about my future so much... And until now, I realize that I have to live and attempt for today. What's gone I can't change, I also can't be so worried what coming next. No one knows what will happen in the future.