Many women experience some degree of “the baby blues” – mildly depressed mood, crying spells, mood swings. When it lasts for more than two weeks and symptoms are severe, we call it “post-partum depression” (click here for a complete discussion). Like you mentioned, exercise is important, but you need professional help – now! If the baby blues, or depression, get to the point that you are having thoughts like this, then a short course of an anti-depressant is probably a good idea.
“I had my first baby 9 months ago and recently I started having depressive moods especially towards my husband. I probably suffer from postpartum depression. I feel listless, easily agitated, fatigue, lack of interest, poor concentration and decision making. However what I realize too is whenever I feel frustrated or agitated especially after a disagreement with my husband I tend to turn this frustration to my baby. I bit her last week after one of the arguments and felt so guilty afterwards. I have tried having some time on my own and exercising, but it doesn’t seem to help a lot. What else can I do if I don’t want to take anti-depressant?”