Dec 18th 2015 I Had My Last Of 15 Treatments

Dec 18th 2015 I had my last of 15 treatments of radiation. While having the treatments my right arm started having pain. The dr said he didn't know why, it shouldn't be from radiation but he would take the blame since I was having that done at that time. I went back to see him on Feb 18th 2016, he had no reason why my arm was still hurting. I am having a scan March 18th to see if all the cancer is gone. I had Nodular Lymphoyte Predominant Hodgkins Lymphoma. On my right arm I feel a lump almost like I felt under my arm, my question is could that be lymphoma as well?