Swelling beneath armpit

Age 65 and recently had a quarter inch skin tag removed from right armpit by dermatologist. Now experiencing swelling beneath armpit. Dermatologist and primary care doctor say it is just fatty tissue; however, this area was not swollen prior to skin tag removal. The area is puffy, numb and feels like a towel is stuffed under my arm. I have had ultra sound and MRI procedures done on the area with results allegedly showing only fatty tissue. There is no pain, soreness or redness associated with this area, but it is rather large and quite uncomfortable and I still have no explanation of why it developed. Has anyone else had such an experience, or have suggestions where I may turn for answers to this condition?