Brief Answer:
Possible that you might be having throat infection

Detailed Answer:
Hello,

Thanks for posting your query,

I am pleased to be able to assist you with your health query.

From your description, I could think of one possible cause which is strep throat or pharyngitis (barium meal can not show any abnormality if this is the case) and if you had some blood test such as CRP, CBC, ESR etc we might have had a more clear cause of your problem. Also I do not think thyroiditis could be considered given that you have not mentioned some other symptoms related to thyroid gland inflammation.
Given that pharyngitis is a relatively simple diseases to determine even without tests, I want to believe that your doctor had another cause in mind and with the little information I got at hand, I will be unable to tell what other possible cause besides just stating my suspicions. The symptoms you are presenting is known as odynophagia (painful swallowing) which could be caused by a wide range of diseases such as ulcers and mucosal destruction, upper respiratory tract infections, immune disorders, epiglottitis, cancers, and motor disorders etc.
You will need some antiinflammatory medications such as ibuprofen, diclofenac etc to get rid of the pain and fever and if infection is responsible then a course of antibiotics will be helpful.

Hope this helps and wish you the best.
Dr. Nsah

---