Had a enlarged lymph node on the left side of my neck for months

[M1llerTim3360]

I am 22 years old and don't smoke and barely drink. I've had an enlarged lymph node on the left side of my neck for a few months now as far as I can recall. I got a ultrasound on it and the results came back as nothing out of the ordinary. They said my body just might be fighting an infection I don't know about. I am still extremely worried because of how long it has been enlarged and the left side of my neck feels a bit stiff as well as the right side but not as much.. And I am just wondering what the infection that my body can possibly be fighting. I don't feel sick at all. I haven't been sick in years actually. Can it be due to a deviated septum and polyps and blockage in the nose? because I was recently diagnosed with that. There also was a point when I've been having pressure/migraine headaches but that seemed to have went away. I am just worried about this. Would an ultrasound pick up cancer if it was abnormal?