Enlarged lymph node

My 4 (nearly 5) year old whippet has got an enlarged lymph node on his neck (about the size of a grape). He has had a FNA which showed no signs of cancer but infection so he has been on antibiotics for 12 days. He finished the course 2 days ago but the lump is still the same size. I have contacted my vet who advised more testing. Should I wait to see if it goes down as he’s just finished the course of antibiotics or just book him in?