There are many potential reasons that you could be having swelling at the base of your neck. The list of possibilities would be narrowed down considerably if there was more information available to help with narrowing the field, such as how long the symptoms have been present and whether or not you are having other symptoms as well. One of the most common reasons for swelling at the base of the neck is to have muscle cramps that can often come because of stress. If you have been having a head or neck infection in the recent past, lymph nodes can often become inflamed and the swelling and irritation can be obvious as you feel the back of your neck (although it is usually more common for upper respiratory tract infections to have lymph nodes in the front of the neck rather than the back). If you have a history of skin cancer, another concerning thought would be that there may be some involvement of that site as well (although this is much less likely if you have no history of this). As you can tell, there are many reasons, and it is important to speak with your doctor
. Please speak to him or her soon.