Hey Zom, my ex-wife experienced this and it's actually far more common than most people think, because most people don't talk about it. I strongly urge you to talk to your family doctor as a start. (Obstetrician if you have access now would be good too) In most cases, that's the only level of care you are likely to need and it's deceptively easy...for the Doc. For you, it may seem really difficult to even take that step to call, and ask for help. That's often part of the nature of depression.
Just to reiterate. This is common, and it's usually fairly easy to treat. Don't expect an immediate fix. It takes a bit of time but I'm not qualified to comment on how much. One other thing- it's also common for a PP Mom to feel guilty about these kinds of feelings. I'm a big fan of feeling guilty- but only if you've done something wrong. You haven't. Please call your family doctor today.
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A Parent, old geezer, and occasionally right. Good judgment comes from bad
experience, and a lot of that comes from bad judgment.