Yea, you could say that. Even though Jeny corrected harder for complicated, I think that harder is fine. What I would change, however, is the first part of the sentence to make it sound more natural. The sentence how it is now seems to be missing something. Instead of: You don't do anything but make things harder I would say: All you do is make things harder Even better: All you do is make things harder for yourself.

You don't do anything, but make things complicated.