My dog had her pups just over three weeks ago and last night I noticed she had a small amount of dilute colored red discharge. I haven't noticed any before, she didn't seem to have any today either. Is this normal or do you think she has an infection? I also noticed she has a dry nose this morning. She's eating well but seems a lot less energetic since shes had her pups.

I would expect a discharge for anything up to two months after pups are born.  This is the Lochia (same in humans).  As long as it is not offensive smelling, red to brown (green staining normal in first few days) then it is normal.  See here in ref to humans http://en.wikipedia.org/wiki/Lochia