Hi Ratbag and welcome to this forum of a wealth of information and support from others who understand how you are feeling .
I also was diagnosed with triple negative BC in late October 2018.
I can’t help you with your current issue with a prolapse, and I’m sorry to hear about what you are going through.
I had a hysterectomy around 8 years before my diagnosis, my ovaries were left intact, and I had to be careful of how much exercise and straining I put on my body in the early stages after surgery. Mind you my surgery was like having a C section birth, so I could hardly walk for weeks.
I did see a Physiotherapist to learn how to do pelvic floor exercises to try and prevent a prolapse, when I thought that things didn’t seem quite right in that region, on several occasions I found myself pushing things back inside. Pelvic floor training helped me, I didn’t or haven’t had any surgery to have it fixed.
I hope that you will also have success in being trained by a physiotherapist on how to do your pelvic exercises correctly.
Happy to have a chat anytime if you have any other questions
Wishing you the best, sending virtual hugs xx