During your visit with your veterinarian, did they do any blood work, urinalysis, X-rays, etc. before prescribing the medicine?  Are the swollen neck glands on both sides or just one side?  Are there any other glands around the body that are swollen?

Swollen glands and a fever that high generally indicate a pretty active response to an infection and the causes that might lead to this are too numerous to list here.  Lab work would help to eliminate a lot from that list.  Once a few good possible diagnoses are left, more can be done for your dog.

Helpful Buckeye