R- side neck pain, decreased appetite, weightloss, drenching night sweats, on/off thyroid swelling dry cough. Clean blood, x-ray, & u/s. Not lymphoma?

Many possibilities. Lymphoma usually isn't painful, but the other symptoms could fit. However, there are a number of other possibilities. The thyroid swelling is suspicious for thyroiditis. If that is ruled out, ct scan of neck, chest, abdomen and pelvis may be helpful, or possibly a pet/ct. Various infections, and autoimmune diseases can cause similar symptoms to malignancies.
Evaluation. Other condition like autoimmune disease- including autoimmune thyroiditis, lupus ; or infection like lyme's etc- should be considered, besides malignancy. What kinds of blood works have you done? How much weight did you lose? See a hematologist/oncologist if you are concern. We'll see what work- up you did and whether it is enough to say that the blood is clean. What is your tsh? Anti tpo ab? Etc.