Thyroid nodules are common. The majority are benign. I do not know what could also cause swollen lymph nodes but it is quite possible the two issues are unrelated. A lot of people have thyroid nodules (lumps on their thyroid) and I think a lot are found incidentally when checking other issues, like your lymph nodes. They are not necessarily related to those other issues.

I will also say that thyroid cancer is a pretty mild form of cancer, so even if you do have it, it isn't necessarily as worrying as you might be thinking (not saying that it's in any way likely you do, but just to consider the worst case scenario). I had thyroid cancer - diagnosed just under two years ago - and I basically had my thyroid removed, was off work for a month and then went back to life as normal. The worry was the worst part of it.

Among younger people, the most common form of thyroid cancer has a near 100% survival rate and they rarely use chemotherapy or radiotherapy. What happens is that they remove your thyroid and if they are concerned about recurrance, might also do radioiodine therapy. The latter is basically just a matter of swallowing a capsule. It is annoying because you are radioactive after it and have to stay in hospital for two or three days to remain away from other people and after that, you sort of have to socially distance for about two weeks, but that's all it is - annoying. It doesn't make you sick or anything. Well, I have heard some people feel nauseous after it for a couple of hours. I didn't though. I didn't feel anything at all.

Feel free to ask if there is anything else you want to know and I hope you get good results.