What Causes Pain Post A Surgery For An Open Book Pelvic Fracture?

I recently had surgery for an open book pelvic fracture. I am about 12 weeks post surgical now. At 10 weeks the prosthesis (plate) broke. I am having slight additional pain, particularly when I am laying down and trying to move my right leg. Also when I get up in the morning I can feel things moving around. Is this common, and is it common for the plate to break?