I have NO privacy! And I am treated like garbage!

My fiance and I live with his mother to help her take care of his grandmother who has Alzheimer's. We are in the process of moving out, and planning our wedding at the same time. For now, there is not a lot we can do in regards to getting our own place. We are leaving the state in a few months but MIL needs us to live with her to care for grandma. My fiance works full time and I watch Grandma. She requires constant care. We sleep on the couch and have been for 5 months. We're getting married in August, in a different state. And I am losing my mind. We have no privacy. We haven't had sex in MONTHS. Grandma follows me everywhere. I do all the cooking, the cleaning, the medication, the bathing, the laundry, EVERYTHING. I am only allowed to leave the house for 2 hours on Saturday's. So I go a week or more without even leaving. I'm never alone. I smoke, so I go outside for 5 minutes here and there but grandma follows me out. And she has bad lungs so I can't smoke around her, so I don't even get THAT anymore. On top of all this, my MIL is always on my back. If I'm not sitting by grandmas side 100% of the time, I'm "slacking". If I'm sitting by her, but I'm on my phone, I'm "slacking". If I don't have grandmas laundry done BEFORE 9 am, I'm "slacking". I'm seriously going to have a meltdown. But in order to have a meltdown, I would have to excuse myself to the restroom and I'm not even allowed to do that! Does anyone have any advice to offer? My sanity is on the line here. Thank you in advance.