Well in cases of Severe Depression, there are people who can't cry. Hell, for me, depends on the day. Sometimes I can't cry, sometimes I can. Guess it depends on how my mood is and what the situation is.
St.John's Wort MAY help, but make sure you don't give up too soon. I think it'd take AT LEAST a month to kick in, so don't assume its not working after a couple weeks. In fact, maybe talk to a Natural Health product store worker about it, if the label doesn't tell you anything.
If your depression is too strong, it might not help, from what I've heard, but I wish you the best with it. Feel free to PM
me if you want to talk.