I had a mastectomy one year ago and now i am noticing swelling and pain in my arm. what could be wrong and what do i do?

Possible lymphedema: It is best to see your oncologist. Arm swelling most often is from lymphedema which can be evaluated and treated by a trained specialist. Other problems however do need to be ruled out which is best determined by your oncologist.

See your surgeon : Swelling now maybe a sign of lymphedema due to the previous surgery blocking efflux of fluid out of your arm( previous lymph node removal or radiation to your armpit and breast). Pain now without previous discomfort or burning is unusual therefore you need to be checked out first by the surgeon for infection or recurrence. Once cleared - lymphatic massage treatments.