Prolapse can be one source of pelvic pain. There are lot of women that sit in my office and tell me they experience a dragging sensation low and deep in the abdomen. Some ladies report a sudden onset of severe sharp pain with a heavy lift or push, (eg. the lawn mower through long grass). Why there is pain most likely due to ligamentous strain, just like it might hurt when you sprain your ankle.
For a grade 1 or 2 prolapse pelvic floor exercises can be very effective in relieving the symptoms of pain, discomfort and or bulges at the entrance to the vagina. If you have a significant bulge at the entrance to the vagina it best to see a GP who will guide you from there.
How does the pelvic floor support the pelvic organs. Imagine your pelvic organs are like boats sitting at dock, the boats are held in place by ropes and supported by the sea. The ropes are like your ligaments and the sea is like your pelvic floor. If the sea dissappears, so does the support fro the boats, your pelvic organs. And a prolapse is a possible outcome.