Lift & exchange of implants 6 months ago - fat necrosis, ruptured implant, or something else?

I got a lift and exchange of implants 6 months ago. underneath and up the side of my breast near my airmpit, I have a rope like mass. It kind of moves and it’s very hard and painful at times. My breasts haven’t changed shape and there is no rippling. The ultrasound doctor couldn’t say exactly what it is but predicts rupture or fat necrosis. The ultrasound doctor couldn’t say exactly what it is but predicts rupture or fat necrosis. My PS is aware but I wanted to ask here as well for opinions.