What Causes Swelling Of Lymph Node In Neck Leading To Dizziness?

Hi there, my husband had a flu-like virus six months ago and since then has had a chronic swollen lymph node in his neck and has been complaining of feeling dizzy and generally unwell. He has been treated with 4 rounds of antibiotics by his Dr and although the gland has gone down a little, he is still feeling unwell and very lethargic. His blood tests were fine, he s been to the dentist to rule out tooth/gum infection - all fine. What else could it be or what other tests can his Dr do? I m really worried about him - it s not like him to feel so sick. Please help.