I have to agree--probably your tonsils. However, if you are concerned about the thyroid, it is about midway down the neck and wraps around the airway. If your neck is swollen there, which is more easily noticeable from the outside, then it may be your thyroid. If you have a history of thyroid difficulties in your family, I would look less at genetics than the environment your family has been in. Toxins like fluoride and perchlorate will mess up your thyroid. A simple test is to paint some plain ol' drug store iodine on your skin in a visible spot (arm, stomach, etc...) and see how long it takes to go away. If it's gone in a couple of hours (and you suddenly have more energy) then you are really low on iodine. The thyroid needs iodine to function, and chemical can interfere with your bodies ability to take up and utilize the iodine. Check out iodine painting on earthclinic.com.
Best wishes and blessings!