Does this sounds like Flu?

On Wednesday of last week, my boyfriend found a swollen lymph node under his jaw towards the front of his neck (it's localized and is only swollen on his neck). Over the past few days it has increased in size and is tender (painful) to touch. From Thursday to Saturday he became increasingly fatigued and had headaches whenever he moved (he remained pretty active on Wed -Thurs (basketball, running), slept all day friday then played softball. He slept the rest of the weekend (fever, headaches, loss of appetite) went to the doctor's office on Monday and they are doing blood tests and his results were normal. He mono test was negative. He went back to the doctor today for a chest x ray (also looked normal without any other swollen lymph nodes). The doctor prescribed penicillin and stated that if the lymph node  did not go down then he would have to get a biopsy. He still feels fatigued with low grade fever (99-100), but his appetite is back.

I initially thought it was just a flu, but the doctor is alarmed by the size of the swollen lymph node. Is it often to have a localized swollen lymph node and flu like symptoms that turn out to be some type of lymphoma? I'm just nervous for him. What should we expect?

As a note he was tested for all STDs in March and was clean (he tested 12 weeks after any possible exposure to anything).

[JDS2805]

Lymphoma normally causes some abnormalities on a CBC but the only gold standard test for lymphoma is a biopsy of the lymphnode.Is the node sore and tender or painless? If all the other tests come back normal and he continues to feel this way he may want to consider seeing an Internal Medicine Doctor