need advice...

So I'm staying with my sister and her fiancé for three months until I go back to college in august. I'm trying to save money but all my money is going to the rent that I have to pay them. I work at subway, at night sleep in mornings. Do chores around the the house, to help out, oh and I don't have a key to the house so I can't leave the house unless one of them is there. I'm sleeping on a twin size air mattress that's used for camping I have my clothes on the floor because there is no where for me to put them, and I get a third of a room shared with a deep freezer, treadmill and a salon chair. Ever morning I wake my back feels like meat, and my legs feel like someone is poking me with Needles from three weeks of sleeping on the air mattress. Sorry about the mess I can't really do much about it. So sure I continue paying and doing the chores or should I just leave and go back to my parents house?