I agree with 898_1; get the antibody tests. Those would be Thyroid Peroxidase Antibodies (TPOab), Thyroglobulin Antibodies (TGab, and Thyroid Stimulating Immunoglobulin (TSI). The TPOab and TGab will confirm/rule out Hashimoto's Thyroiditis; the TSI will confirm/rule out Graves Disease. Please note, that some people have both, so you need to be tested for both.
In addition, can you post whatever thyroid tests were done and supposedly "normal", along with the reference ranges, since these vary from lab to lab, so must come from your own lab report?? That would help members comment more fully on your situation.
Many of us have inflammation in our thyroid, so you aren't alone.
this may sound like inflammatory process; you may need to have blood test for antibodies/ ESR rate