Thank you for all the information,
There is likely an inflammation as you thought.
An infection is possible too.
Sometimes,it can be enlarged lymph nodes.
This usually occurs from any previous inflammation , allergy, infection in its draining area.
An examination is necessary at this point as it is increasing in size.
Much tests may not be necessary.
Blood count, ultrasound can be taken.
Antiinflammatory pain medicines like motrin or naproxen can be taken to reduce the pain, if there is no contraindications to them.
I hope this information helps.
If there’s anything else I can do, please let me know.
Please rate my answer excellent if you are satisfied with it.