How Can A Painful Neck Swelling With A Knot Be Treated?

I have a swelling in my neck on the left side. I've pin pointed it to what i think is the retropharyngeal lymph node. It happens about once a year, but this time it's been going on for two months or more, theres a knot and it's tender to the touch also when i swallow or my head is turned to the right it can be very painful.