It is with complete honesty and evident internal and external experiences when I say "follow your passion".

It is a concept that many successful (by his/her own measure) struggled with, so you aren't alone.

Perhaps you could ask yourself few, but not limited to, simple questions and expand them further.

* What would you do if money isn't an issue?
* Are you investing personal time and effort to build on depth and variety in your field, not because of money, but of curiosity, challenge and fun?
* If your work isn't quite your passion, what steps have you taken to fulfill your passion?
* Could you bridge your passion and work?

Passion often goes unnoticed. Nonetheless, it could also be developed. Read wide and randomly (foreign literature). If you stumble onto something interesting, go deep. You'll be rewarded.