Hi Celtic,
I'm sorry that I can't help with what could be causing it, and I've not given birth so my advice isn't on that level either.

I had anorexia as a teenager, and for weight restoration I was on a supplement called Sustagen (which was all I had for a while), which you can get from the supermarket, which you mix with milk and is really good to provide nutrients, and it sounds like you could really use it now. You could check that out if you are able to get down liquids? A few sips every couple of minutes, and you know you are getting at least some of the nutrients you need while you work out whats happening?

HTH and hope the drs sort this out for you soon.