Life is meaningless... what must i do?

Find a mentor,: become a mentor, associate with a volunteer organization who's interests are in line with yours, consider finding a clergy or clergyman aligned with your ideals, consult with a mental health counselor...

Start with your GP so that a comprehensive assessment takes place as many times medical conditions create the premises for depression. If nothing medically treatable is found, your GP may be able to further coordinate locally and identify resources of help for you.