Armpit lump swollen now gone

jrt74

Hi all. I had a unilateral mastectomy in November for stage 0 DCIS, low nuclear grade with a sentinel node biopsy. All came out clear. Sunday I had a hardish pea size bump under my armpit that was quite painful. It’s since gone away with some residual pain. I called the doctor and have been waiting for a response from them, but does anyone think this is just something to not worry about? Can lymph nodes swell under the armpit randomly after that? I can’t imagine it would be a cancerous condition given the testing and surgery being only 7 months ago. Thanks in advance