I don’t think you did anything wrong but I’m not sure why we are not warned that this could happen or told how to prevent it with at home simple exercises.
Just now starting PT and the therapist is trying to evaluate if the discomfort in axila is due to lymphedema. I don’t know if you can develop lymphedema without having had a lymph node resection or biopsy. Question is Can XRT alone cause it. Diagnosing this should not necessarily be in the physical therapist’s wheelhouse so I think now i will contact my surgeon. Will keep you posted.