The most common cause of swollen sublingual gland is a Staph aureus infection. This can be acute or chronic. Recurrent infections can lead to scarring and inflammation of the duct.
Treatment would be to massage the area for signs of pus which can be cultured. Swabing may be helping for diagnosis.
Other option can be the presence of a stone.
Treatment is usually antibiotics, warm compresses and a salt water mouthwash may be helpful. Its possible you have a reservoir of infection which occurs in either the ear, throat or the various ducts so a longer antibiotic course than usual may be required.
There is a special sort of x ray which allows a wide view picture of this area to rule out presence of stones, your doctor or dentist may be able to organise this.
Ensure that you are eating well, plenty of fruit and veg to assist your immune system. If the problem persists you can request a differential White Cell Count from your doctor to check that your immune system is functioning normally.
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