A dentist might be able to help you figure out if it's the wisdom tooth that's causing the lymph node swelling. Does the tooth cause you any pain? An absessed tooth can surely cause lymph node swelling esp. under the jaw if the infection is trying to spread past the confines of the tooth's socket and is draining debris and white blood cells through the lymph system.
A dentist can evaluate all of your other teeth too to see if any problems relating to infection are brewing. I know when I had a tooth abcess, I had jaw, cheek and eye pain too. Headaches. Referred pain from the tooth, fortunately which left me alone once the tooth was treated.
I think your doctor is trying to rule out serious illnesses which can cause lymph nodes in the gland to swell(but only in a minority of cases) to be on the safe side. Problems with ears, sinuses are often evaluated as well.