Oh, m&ms, I'm so sorry to hear about this nasty bug you've contracted. Shigella sucks! I've never had it but had very similar bacterial or parasitic infections. I remember riding the barge across Lake Titicaca from Bolivia to Peru, just feeling like I wanted to die...and then the bus ride, having the bus driver stop every few minutes so I could go explode on the side of the road. Oh, I do not envy your position right now...I feel for you.
I hope you are taking Cipro, because a lot of Shigella organisms are becoming resistant to the typical sulfa drugs normally given. Do you have access to any kind of probiotics? I would stuff yourself silly with those while you are on the antibiotics. That will help dissuade the C. diff from overtaking your system.
It is so hard to keep going, I know, when you are in the midst of extreme poverty, watching people take dumps on the sidewalk, not having any of the typical "comforts" of home, being so sick, and feeling scared about how these bugs are going to mess you up. I distinctly remember some very helpless moments, especially being alone in the African bush, where all I wanted was some cold ginger ale and a heating pad but had to make do with warm Tang in iodine-treated water and a 100-degree tent. I'd just be crying from the misery, very depressed. I wish that feeling on no one. I am so sorry you feel this way. Before you think seriously about leaving, though, make sure you get over this illness. Being so sick won't allow you to think clearly.
I'll write more later, I'm at work...hang in there girl!