I've had some swollen lymphnodes this winter so far and went to the doctors a few times for them.
They get swollen when your body is fighting off a sickness, typically an infection.
If you have been having season colds or something like that, or any kind of sickness, it could be why they are swollen.
One thing that my doctor did tell me, was that lymph nodes that are swollen and are tender, it is a good sign, because that is reactionary and means they are swollen because they are fighting off something (as oppose to having lymphoma or something).