Hello Rachel,
SO sorry you are in so much pain.
I know what that is like. When I was taking painkillers before my surgery, I took 100 mg stool softener in the morning and again at night. I also took 1 dose of Miralax in the morning and I ate some raisin bread with 2 extra chopped prunes at night. I was also terrified of constipation, but even with the painkillers every 4 hours, I was able to go every morning after drinking some coffee.
Also, the last couple of days before my surgery, I did not sit at all. I layed on my belly if I wasn't standing or moving around. It's a crazy struggle and I had to truly advocate for myself, so do your best to get in to see someone and get fixed as soon as possible.