back of the neck symptoms are not likely related to thyroiditis
the ct scan may not confirm exactly why you are feeling a 'lump' -- but will tell you if there is a non-thyroid mass, etc that needs to be considered
The evaluation is to do a FNA biopsy of dominant nodules (these are most likely areas of increased chronic inflammation from hashi) -- but needs to be done to test for cancer.
Then, if the symptoms persist, would see a surgeon to evaluate if the thyroid nodules are the likely cause -- if so, then thyroid is removed surgically.
The sed rate is not usually elevated in Hashimotos of 11 year duration. If this is related to thyroid, it may be a superimposed thyroiditis -- which would cause a very tender thyroid which would improve in 1-3 months.