Morph - I've just read your symptoms on this thread and it sounds like you may have bipolar II (the less severe form of manic depression where you only get so-called hypomania). Do you think that may be an option? If so, treatment is quite different from ordinary depression and is primarily with Lithium as a mood stabiliser.
Other depressed mums - I've had five attacks of major endogenous depression over the past 20 years, though none postnatal. I've tried a variety of antidepressants (ADs) and it sometimes takes a while to find one that suits you, so don't be put off if the first one you try isn't right. I can't get on with the SSRIs (Prozac, Cipralex etc) but have had good success with the tricyclics (Amitriptyline, Lofepramine etc.)
Remember that ADs are well-researched, safe drugs and aren't addictive. When you're on the right kind and right dose, you won't feel "medicated" but just back to your normal self.
Plus don't forget all the good lifestyle stuff for depression (exercise, decent diet, minimal alcohol, getting out and about etc) and use talking therapies if your depression has an "exogenous" factor (external events have contributed).
Best of luck to you all. Hold on to the thought that your depression WILL resolve itself, either through treatment or just spontaneously, and you won't always feel this bad.