What are the possible causes of my hard immovable swollen lymph node?

[leah9216]

A bit over a month ago, I had a cold that turned into a sinus infection. I went to the doctor and was prescribed an antibiotic. The next day, I found a large bump (maybe .75” across) on the right side of the back of my head. I hadn’t noticed it before and I usually feel my scalp for ticks regularly in this weather so it must have come on somewhat quickly. It is very hard and immovable (feels weirdly like it’s attached to my skull.) It doesn’t hurt except occasionally if I rest my head on a hard surface for too long. I’ve been told it doesn’t look red. It hasn’t grown or shrank noticeably since the time I found it several weeks ago. I thought it was a cyst or something but last week I went to the doctor for my annual appointment and she looked at it quickly and said she thought it was a swollen lymph node. Just tonight, I decided to actually do some research on why I would have a swollen lymph node and I found some things saying that if it is hard, immovable, and has been around for several weeks like mine it could be a sign of cancer and I should see my doctor. However, my doctor felt it when I saw her last and clearly she didn’t think it was a big deal.

So mostly what I want to know is:
1. Is it possible the sinus infection is causing the swollen lymph node even though my symptoms have been gone for about 3 weeks?
2. If a swollen lymph node is hard, immovable, and stays around for several weeks, is there still a possibility that it’s just caused by an infection or is that definitely a bad sign? (If anyone has had a lymph node like this that turned out to be nothing bad, feel free to share for my piece of mind.)

[leah9216]

Oh also, I just remembered maybe I should say that these past couple days I often feel slightly lightheaded and like my head and body are buzzing or trembling when I stand up. No idea if that’s relevant or if it’s just because I haven’t been eating as healthy this week as I usually do.