Sorry to hear about your condition but I am glad that you are seeking medical attention for the same. These lumps might have been there for sometime but they must have become evident once you shaved your head. In any case because of your diagnosis of breast cancer
, it is better to have them evaluated by the oncologist
. He might recommend a FNAC for the lumps, which will tell you about the nature of the lumps.
It is highly unlikely to be lymphoma
Hope they turn out to be normal.