hi dear dandsfynn,
welcome to hcm.
Kindly mention ur age, sex, location as this would help me in clinching the diagnosis.
Kindly mention if it is increasing in its size since then and Please mention what medications you are taking for the arthritis
so that we can know if this issue is as a side effect of them.
Please do not pinch it squeeze it. If it starts itching or paining, kindly consult a physician for further follow up and expert opinion to rule out anything serious.