Also, you may want to watch her for signs of Mastitis. (aka 'milk fever') It can also lead to infection and fever which *could* be accompanied by lack of appetite and panting. (Panting is often present when there is fever, but that doesn't necessarily mean that is the case.)
Here is some information about Mastitis:
Canine Mastitis - LoveToKnow Dogs
A couple times each day, hold a warm compress to her belly for about 5-10 minutes. It will help to keep her milk flowing and will help alleviate some of the discomfort she has a result of nursing the pups.
Also, did your vet give her an oral antibiotic to take before and after her whelp to help prevent uterine infection?