Reliability for work: A way to get a head or a way to be taken advantage of....?

One of the reasons that I haven't posted in a while is the fact that during the past couple of months, I have been working a lot. It all started in about sometime mid March, when the "upper echelon" of management were notified that the one of other evening/weekend managers was resigning due to being done with his college degree, his last day at where I work is early/mid May. They had two months to try and find some one as a replacement! They didn't. When the resigning manger left, I got dumped all the hours for the evenings and weekends. Currently for the last month and a half, I have been working 35 to 40+ hours a week, straight! There is another evening/weekend manger but they don't get any hours. They work 10 hours total over the weekend, while I am "forced" to work 18+ hours on the weekends. The reason for 18+ is the fact that I am unable to leave the building for an hour break. I have tried to ask if the "upper echelon" would be able to schedule more evenly. So far I get the notion thrown back in my face, and am still working 35 - 40+ hours a week! I have also not had a weekend off for some time now, I am well beyond the notion of being pisses about it... Some advice would possibly be handy, before...

So I ask: Reliability for work: A way to gat ahead or a way to be taken advantage of?