Hello welcome to healthcare magic, I am sorry that your father is feeling unwell. It is unusual to have a painful throat for 6 weeks. Most cases of sore throat are due to viral or bacterial infection, in the cases of viral infection ( most common) it tends to resolve on its own, in the case of bacterial infection antibiotics may be necessary. Bacterial infection usually responds quickly to a course of antibiotics Allergic rhinosinusitis may also cause sore throat if the person has a post nasal drip ( feel mucus dripping at the back of the throat) but this is usually intermittent. Another cause would be a growth in the throat , smoking is a risk factor for this. If he does not have a history of allergies and has been treated adequately for possible infection then he needs to be assessed for more serious causes of throat pain