Need advice

I need advice. I am the only one in my entire store who is expected to open and close the store. everyone else does one or the other or neither. I feel like I am being completely taken advantage of and I have tried to talk to my boss about it and her only response is that it won't be for that long but this has been going on for over a year. I am exhausted. it is incredibly hard to wake up at 1am to go to work at 3, then a day later force myself to stay up till after 11 then get home at midnight. my understanding is that years ago when I became manager that ALL managers were expected to open and close the store (one or the other) but again I am the only one in my entire store that does both a certain manager we have does not open and does not close. how is this fair? it makes me wanna quit because I am being completely taken advantage of. advice?