Mild depression - How would I tell if St. John's Wort is helping?

I'm not sure whether I have depression or just feel beat up by having an illness that limits my activities. I do know that I am not enjoying my hobbies as much as I did and actually haven't worked on quilting in nearly a year. I know St. John's Wort has been found to help mild depression, but am wondering how you tell whether it is helping or not? I don't FEEL sad. More like unmotivated? How much do you use and how often?