Hi, Alan. A cancer is not the most likely cause, but it is a possibility.
Is the node freely moveable if you try to push it around?
Would you guess that it might have grown slowly, as opposed to popping up almost overnight? Has the size changed since you noticed it? Any pain or tenderness?
What is your age?
"the lymph nodes on my joints feel a lot smaller"
I'm not sure what that means. You can feel bumps on your joints?
The following things say what probably points to cancer or to not-cancer. The only way to be sure is to have a biopsy where they take out the whole node and examine it. But still, a scan such as an ultrasound can tell a very lot, without requiring surgery.
being moveable = probably not-cancer
it feels a bit hard = either way
popping up overnight = probably not-cancer
not getting bigger and bigger = probably not-cancer
but being rounded tends to being cancer, except if it's under the jawline
some pain tends to probably not-cancer
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A doc might ordinarily say "let's wait 2 weeks to see if it goes down on it's own". But you've already done that.
A doc might give an antibiotic to see if the node goes down. Any possibility of infection in your head/mouth? Any impact as in a sport? Any new medications being taken?
Or a doc might order an ultrasound of the node.
"English is not my native language..."
Your English is very good :)
"Im 19"
Then if it were lymphoma, which it probably isn't, then it would probably be Hodgkins Lymphoma and not non-Hodgkins Lymphoma. You likely know that itching can go with Hodgkins, but then again it can come from immune cells just reacting to something.
The size can go either way.
But all in all, a doctor can see you in person and know if things are suspicious for a cancer, while this talk online is just theoretical and is meant to give an insight into how a doc might think about it.
I would go to a doc without being overly alarmed or worried, and see that as the chance to rule out lymphoma.
Oh, and for the groin nodes... they tend to be larger but I don't think that normal groin nodes would be palpable unless you are very lean.
The most likely cause there would be infection, even from stepping on something outdoors.