I have a soft, movable knot on the left side of my neck. went to dr and they said it isn't a tumor or thyroid. what is it?

A number of things: The possibilities include a cutanueous skin tag (acrochordon), benign lipoma, cyst, infection, inflammation, and malignancy- either primary from the neck (ie thyroid, lymphoma) or metastatic from another location. Mobile soft are usually terms that correspond to a benign condition - skin tag, cyst, lipoma. Duration of mass, change in size, color are also important. Best to visit ENT if concerned.

Hmmmm: Well, it could be a number of things. I would suggest seeing an otolarygologist who can perhaps more accurately give you an idea of what it is or suggest a test that may help define it. A ct scan or perhaps a thyroid ultrasound likely will give an answer if the ENT doc cannot tell you.