Hi.
A week after lumpectomy, pain can still really persist since during this time, the healing process still continues. The time it takes for the pain to go away completely varies from person to person and there is no cardinal rule. However, we can reasonably expect all the pain the disappear 6-8 weeks after the procedure (but I have a patient who still has lingering pain even 4 months after the operation).
To aid in the healing, make sure you get plenty of rest, but at the same time talk to your doctor about rehabilitation exercises to fully regain functionality. Also get some prescriptions for standard pain medications.
Regards.