It is possible that this could be thyroiditis (inflammation of the thyroid gland).
It is recognised that people known to have autoimmune disease have an association with increased frequency of having/developing more than one autoimmune disease.
There is a type of autoimmune disease called Hashimotos thyroiditis.
Thyroiditis can have other aetiology such as viral, bacterial or by drugs.
It is equally possible that it may not be the thyroid, but lymphadenopathy.
In any case it would be prudent to see your GP to examine the neck. If your GP thinks it is thyroiditis they will need to perform blood tests to asess thyroid function and identify the appropriate treatment.
I hope this information is useful, feel free to reply for any clarification