Hello, As per your complain persisting metallic taste under the tongue can be due to infection in the salivary gland leading to discharge of infectious fluid known as pus and it can be a common cause of metallic taste under the tongue. Other causes of metallic taste under tongue can be a side effect of any medication, dental and gum infection, ulcers etcetera. Dull throbbing pain on the side of the head can be a radiating pain from the gland or can be due to other causes like stress, migraine, high blood pressure, jaw joint issues etcetera. I would suggest you consult an oral physician, and get evaluated and a thorough clinical evaluation can be diagnostic. As of now, you can take Diclofenac or Ibuprofen for relief from headache. You can gargle with warm saline water. Gargle with an antimicrobial mouthwash. Drink plenty of water. Hope I have answered your query. Let me know if I can assist you further. Regards, Dr. Honey Arora