It could be a few things one of them being a lymph node swollen, they are usually the size of a pea and can hurt to touch and are in the area you described. Are you having any other symptoms like fever, run down etc? Even things such as a hang nail can cause them to swell up.
It could also be a small cyst forming or a ketosis.
If it doesn't go away you should have it looked at, especially if painful.