>I have this lingering thought (or fear) that I don't know what I'm doing with my life, that I'm wasting my life.

Assessing oneself helps to try answer questions, making change is never easy, taking steps to overcome this concern you appear to be finding a way to find better meaning. 

No matter how confident the outside world think we are, we all have doubts about how or what we are able to accomplish with a clear conscious @ericaa, wishing you a wonderful day!