Thank you for your query.
As it is a painless cyst
which has been there for about a week it appears to be as sebaceous cyst. It will again fill up as you have experienced unless it is completely removed surgically. I will suggest that you consult a surgeon who shall remove the cyst under local anaesthesia and send it across for biopsy
I hope I have answered your query to your satisfaction.
Wishing you an early recovery.
Rajiv K Khandelwal