Does St. John's Wort Work? Anything else I can do?

I'm feeling sad all the time and I don't know why. I'm usually miserable, especially around my boyfriend, and I used to be happy, the kind of person everyone wanted to be around. Now I'm often acting psychotically jealous whenever he merely mentions another woman, and he's given me no reason not to trust him. I'm sick of these bad moods for no reason, and I don't want to lose the man I care about because my depression is effecting the way I think and act. Please no smart remarks, I really need some advice. Seeing a therapist is out of the question, because I don't have that kind of money. And I'd like to avoid anti-depressants if possible. Does St. Johns Wort really work? Are there other things I could do to feel happier? Thanks in advance.