Neck lymph node has been enlarged for several months Please help

[M1llerTim3360]

I am 23 years old and there has been a lymph node in my neck just below the jaw line that has been enlarged for months or maybe even longer. It is really worrying me. It seemed to have went down a bit a few weeks ago but now it's back to it's enlarged size. A while ago, I got an ultrasound on the enlarged node and they said it didn't look too concerning. They said that my body just might be fighting an infection that I don't know about. Could an ultrasound pick up cancer if it was abnormal? I am freaking out because what if it is cancer and it's been a while now and the lymph node is still enlarged. What infection can my body possibly be fighting for this long? I have recently noticed that while I'm working, the lymph node seems to shrink down a lot but when I go back home, later on I feel it enlarged again. Can this be due to allergies? I am allergic to dandruff from cats and dogs and I have 3 cats and 1 dog. I aslo haven't been sick recently. I actually haven't been sick in years. I believe I have  a strong immune system. I do have a bit of a cough though and I constantly have a stuffed up nose because I was recently diagnosed with a slight deviated septum and polyps plus blockage in the nose. I always have to breathe through my mouth. I was put on steroids and nasal spray and my nose cleared up a bit but the lymph node in my neck still hasn't shrunk. Only when I'm at work it seems to shrink. I also have asthma and I've had it since I was a child. Sometimes in the area, my neck feels a bit tight and is irritating and a bit sore. Sometimes my whole neck aches as well. Idk if I'm over paranoid or what but I recently noticed a small lump on the lower back of my neck like it could be another node enlarging. Idk what is going on in my body and what is causing this. Can it be the constant weather changes? It has been going from warm to freezing weather in a matter of days. My nose tends to get stuffed up during the day too. I just hope this is nothing seriously life threatening. A response would be appreciated to help ease my mind.