it is not swollen it is just very painful.
If the lymph node is not swollen and it hurts, as much as I know it might be two things. First is a sinus infection. Have you had any problems with sinuses before? It usually manifests as pain around eye and nasal cavity, and severe headaches. It can get very complicated.
Second thing is something that you can’t know until you run some tests. It might be a form of some seasonal allergies. Are you allergic to anything? From cedar to peanut butter, anything can affect this if you might be in near contact with it.
However you should be feeling pain on lymph nodes on both sides. You said that one is not swollen. What about the other one? Have you noticed any swelling on other lymph nodes?