feeding

Courtney
So my 7 week old got the stomach bug on Thursday night. Ever since then she really isn't eating very much. She will sometimes take 4 oz and other times barely 2 oz. She is still having wet diapers. Should I still be concerned. She just had a massive spit up, trying to figure out if it was spit up or throw up. Is there anyway to tell the difference? 
Looking for any advice.