lymphnode enlargement

i know aperson whose submandibular nodes were enlarged for past 8months he checked a doctor he had made ultrasound neck and said size of both nodes were about 3cm approximately so no need to worry it might be some ora infection so he asked to maintain oral hygiene but ultrasound also said about 4.5mm size of another node in posterior triangle of neck patient is 20yrs old what to do how to proceed pls help me friends will it be any kind of lymphoma if so what about treatment pls reply me?????/