Brief Answer:
Probably caused by inflammation somewhere

Detailed Answer:
Hello,
the data you've provided are not sufficient for a complete and specific answer but I'll share with you some general thoughts about lymph nodes on the neck. That's the best a doctor can do, given the lack of information.
Important clues would be:
- position (where on the neck) and size of lymph node
- associated symptoms including fever, respiratory tract symptoms, etc
- relative medical history. For example history of lymphoma, HIV, tuberculosis etc
- teeth and mouth problems
Since you 'feel' it, I suppose you mean it's tender or even painful. Most cases of a tender/painful lymph node involve some sort of inflammation. Upper respiratory tract infections are common causes but teeth problems and dermatological infections in the area may also make a lymph node bigger and tender.
Malignant causes include hematologic malignancies and cancer.
'Feeling' the node is a good sign in that regard because malignant nodes are usually asymptomatic.
I should also note that a week is considered a very small time period regarding lymph node enlargements. It is very likely that the node will stop being tender during the next few days and you'll forget about it.
I hope I've addressed your concerns!
If you need more details on the subject, please ask again, providing more information.
Kind Regards!

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Brief Answer:
You'll need clinical examination of the node

Detailed Answer:
Hi,

Thanks for your query.

So no pain, no sign of inflammation. If I understood your description the node must be close to the thyroid gland. It is possible that the 'node' is an enlargement of the thyroid itself (or a nodule within it). Other possible causes include what I've already mentioned in my previous answer.
Since there is no sign of inflammation, one should look for other lymph nodes or organ enlargements (mainly axilla, groin, spleen, liver). Generalized asymptomatic lymph node enlargement or organ enlargement may be a clue for a generalized cause including hematologic malignancies, autoimmune diseases etc.
Also palpating the 'node' should give us some clues. A rock-hard sensation on palpation is a clue for malignant causes. A not so hard but firm sensation (like a tennis-ball) could be either benign or malignant). Anything softer than that suggests lipomas, cysts and other benign causes. Also a moving mass is preferable to a mass that seems attached to the surrounding tissues.
In any case you need a careful clinical examination by a doctor. The doctor can make a likely accurate assumption of the nature of your problem. Further testing might be needed though (biopsy).

I believe your question has been answered. If you need me to clarify anything, feel free to ask.
Best wishes!

regards,

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