My Mother with COPD and osteoporosis refuses outside help. What to do?

I rented out my home and have been living with my parents for the past nine months. My mother has COPD and severe osteoporosis. She sleeps in a recliner every night and remains there all day long watching TV. I don't mind being there to help her when she needs it, but I work a full-time job and she can be quite demanding, even calling me at my job to ask me to get something at the store, which can be on a daily basis. I'm quite honestly wore out! She will call me on my cell phone late at night to do some menial thing that she could do herself, but just doesn't want too, or says her lower spine hurts too much to get up and do it, or that she's too tired, etc. My father is very frail, and almost 80 years old, a cancer survivor twice. She feels she shouldn't have to get some outside help, that HE should do it. I feel he won't last long after I'm gone if there isn't some other help. I am only there for 3 more months, as this was just a temporary situation to get mom the medical help she needs, oxygen, good doctors, etc. Ultimately, she refuses any outside help and just wants us to run constantly for fast food, or to the store, errands for her, etc. She can do small things for herself, but if we are there, then she asks us to do it, even to get her a glass of juice. I am so frustrated. What to do?