This could be due to uterine infection, intestinal parasites, or a contagious disease of some sort.
I'd plan a vet visit for her as soon as you can as if she is that ill and nursing her pups they are probably not getting enough nutrition.
You can see if your local pet supply store carries some NutriCal a sticky supplement used to give added nutrition to dogs. You can put it right in her mouth so she has to swallow it.
If your dog appears dehydrated (see if a pinch of skin over the shoulder blade stays stuck in a tent form or flows back down normally when released), has a rectal temp over 103.5F (normal is 100.5-102.5 Fahrenheit or 38 - 39.2 Celsius ), has gums or tongue that look white, blue, gray or yellow tinted where they are normally pink, has a slow color refill if you press on a pink area of gum or tongue, or is becoming lethargic and non responsive to you then you may want to get the dog in to see an emergency vet if one is available in your area.
This site may help you locate an emergency vet if you need one
http://www.vetlocator.com/hotline.php
Hope this helps you!
Dog Expert:Rescue, Train,Breed,Care
30+ yrs dog home vet care & nursing, rescue, behavior&training, responsible show breeding, genetics