Thanks for writing your query to us.
Submental lymph node is located just below the chin.The lymphatic drainage
from the tip of the tongue, lower lip,floor of the mouth,skin of cheek,salivary gland
, teeth will go to the submental nodes.
The lymph node swelling can be localised or generalised that is swelling in other lymph nodes in the body. Three weeks is a long time. As the infection subsides the lymph node swelling also decreases.
Since the swelling is still there from 3 weeks i would advise that you visit your doctor. Your doctor may perform a small test called as lymph node biopsy
& examine the lymph node biopsy sample under microscope to find out the exact cause of submental node enlargement.
Wish you a good health.