Likely a prolapsed uterus. Sometimes it shrinks back in and sometimes it doesn't. Some fish have lived with it and most will die. You can research a little more. I have read so many things about it one even mentioned somehow putting it back.
With your fish already looking to be suffering, you might want to consider some reading on euthanasia. It is a sad part of fish keeping.
Here is the Sticky link -
FW & SW
Favorite tank right now - 72G Bowfront Wadai Tetra, Cardinal Tetras, Ghost Glass Cat Kryptopterus bicirrhis and Clown Loach Cory haven
New to FW fish? First tank in a long time or EVER??? Need some info on keeping fish?
Start here - Aquarium Advice Article