Total thyroidectomy one week ago. bulge formed below incision. ok? how long until it goes away?

Check with surgeon: The most likely cause is some temporary inflammation of the tissues under the incision. A hematoma (blood clot) or fluid collection is also possible. Less likely causes would be infection or scar tissue. If the area is red or tender, you need to see the surgeon right away. If not, typically the incision is checked at 1 month after surgery, by then it should be healing very well.