When you have a prolapse you need to be careful about the sorts of exercise you do.
Because some will absolutely make it worse. Anything that pushes down on the lower abdomen or pelvic floor won't help, like situps.
Similarly you have to switch to walking on the flat not running. As running bounces the pelvic organs up and down.
If you've overdone it you might feel heaviness down below by evening time.
Don't push or pull furniture around. Don't lift heavy suitcases, use wheely ones. Divide shopping into smaller bags not one big one. Get some one else to hoover if possible, at least for the first few months. That heavy pushing against force is what you want to avoid if poss.
All the above help it gets better or no worse.
Regarding sex, it all goes back in place when you lie down. Things can feel different down there after a baby, but it does improve. Especially if you do pelvic floors.
But the physio will help you do those correctly and check your progress.
Having done pelvic floors before the birth is no guarantee of preventing a prolapse, so it's nothing you did to cause this.
Don't blame yourself. It just happens.
Some doctors are very dismissive and they don't understand the emotional impact.
There's a website run by an Australian physio called Michelle Kenway if you Google her.
There's also some good therapy videos on YouTube by therapyinanutshell by Emma McAdams. Some good free videos there to do with coping with negative thoughts.
But don't be pressurising yourself to get fixed really fast. Take it slowly. Best of luck and don't let it cloud your enjoyment of your new baby.