A couple of answers.. VB
I wouldn't be attempting to sleep on your tummy until you get clearance from you OS.
When you sleep on your un-operated side, do you have a pillow between your legs? This is to stop the operated leg crossing the midline.
For sure you will feel muscle pain when standing or walking, those muscles are still weak. At 2 weeks post, I was doing absolutely nothing.. except bathroom visits, bed to chair, chair to bed, elevating and sleeping..
Why do some patients have longer incisions? Well when the surgeon first looks at your pre surgery x-rays, they have a pretty good idea of the damage or issues they have to repair, so they do all sorts of Pre surgery planning themselves on how big an incision it will be..
My OS knew that my surgery was going to be very complex, so I have a 10 inch incision with 39 staples.. I was happy that he had such a good view, because he had a lot of repairing to do.. Result.. Perfect!