Pain from armpit to behind nipple

Hi! For a week I've had a sort of burning pain when i stretch my arm over my head that goes from my armpit to my breast and under my nipple. Now my breast hurts to touch. At first I thought it might be muscle but it's different. It's been 2 months since i finished radiation and have had no other problems since then.
I've had a lumpectomy and then sentinel node biopsy (2 nodes, both clear).
Is this normal?? No swelling that i can see and i exercise a bit