Dear@Louise64
I had a mastectomy not a lumpectomy but it appears that post operative pain (sharp, not an ache) is not unusual. Nerve endings can be damaged and settling scar tissue can also cause problems. I’ve only had a bit of scar tissue discomfort, which has been quickly resolved with massage and stretching. As with anything new (and certainly anything painful) it’s worth getting it checked with your surgeon or oncologist, but there’s a sporting chance it’s annoying but not serious. Best wishes.