Kim, how could anyone read your message and then say : No, of course you don't need help ? Surely it's obvious, so the more interesting question would be : why have you hesitated in seeking the help you so obviously need and deserve ?
Post-Natal Depression is common and nasty, but usually responds really well to the proper treatment. Don't waste any more time as there's no need for you to continue to feel so wretched for longer : do arrange urgently to see a good local psychiatrist for a proper in-person assessment, diagnosis and a discussion of treatment options.
He/she will probably suggest using an antidepressant drug, which could indeed be really useful, but from your description of finding returning distressing memories of things about your childhood, I strongly suggest that you also ask to be referred to good local psychologist for psychotherapy as well, preferably using the CBT method, to explore and help you control and work through whatever emotional issues have been arising during your depression.
Don't blame yourself for temporarily not being able to make yourself feel good "naturally" : with appendicitis you can't make yourself feel pain-free "naturally", but you see a good surgeon, and get better.
Feeling worthless is a natural part of the chemistry of depression, and this inaccurate self-assessment will correct as your chemisry corrects.
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