Constipation can be a side effect of removal of your gall bladder (or even from before it was taken out). Usual laxative remedies, like prune juice, fiber, aloe vera can all be tried. I've also heard about bile salts, which are supposed to replace the bile that you no longer produce. I've only read about them online, and I think you have to order them online, but you may want your mom to check into them for you.
I don't know what kind of private school you are going to, but when I was in private high school, there were a couple of kids who had to do their lessons and work from home. I don't know if they had teacher contact or not, but someone probably did call them and talk to them. I went to a very supportive school. One girl was out for at least a month, I think, though, two or three, with menegitis, and one boy fell off a cliff and was out for a couple of months while his femur repaired a bit. We had one girl, who was a boarding student, who got bit by a copperhead a few weeks before her graduation and she was put on bed rest and took her exams in her dorm room. And after I left, a guy in the class behind me fell off a roof and became paralyzed--I know from the waist down, but I think he was paralyzed in the arms too; I don't think he ended up needing a breathing machine, though. Anyways, they got him through school and he graduated. So, at least in my school, there were a number of kids who got sick or hurt and the school got them through their lessons somehow anyways. It being a private school that you're paying for, they should work with you better than a public school. Do you have any sort of academic advisor or mentor? That would be the person to go to first about your problems. If not, then set up a meeting with your academic dean and tell him/her what your health problems are and see if there's a way to either make going to school easier on you, or find a way so that you can study partly or fully from home.
Next year, if your mom can't afford the school (most private schools have scholarships; be sure to ask before giving up), then you should look into public school and what sorts of homeschooling/tutoring programs they offer for kids who can't go to regular school. I think Lil gave you a link to a discussion we had with another high schooler who was in one of these programs, so I know they exist. But like all school services, a lot depends on how wealthy your local public school is; the more money they have, the more programs.