Four weeks after my lumpectomy I saw my GP because I had developed a rash on the breast and by the site of the axillary node clearance. When she examined me she said she could feel a lump at the operation area. On being transferred to A&E the surgical team said there was no such thing but slightly swollen tissue. Perhaps this is what you are observing.
I would not worry. It takes time for the breast to settle.
A&E do not know everything. I recently had bad experience about something else. They try to convince you and themselves they know all. Ask for second option. Scar tissue can cause lump, so they didn't know. I have had such removed from different operation.
A week post op is still very early. Is your drain still in? It could be blood pooling in the area or just scar tissue. You will still be under the breast cancer nurses so maybe ring them? I'm 9months post smx and happy to chat further if required. Hugs
