Working at STAPLES SUCKS A little!

Today i went to my place of employment which is STAPLES. I didn't ahve to work but i just went becuase I needed to buy some art stuff for my little sister that i forgot to buy on Tuesday, when I worked. As soon as Iw walked they were like do you want to work today because we really need you and we were just about to call you. This kind of mad. I know I am a good worker and when they need me they can count on me but they can't always and constantly count on me. At the moment we have about 7 cashiers when we are suppose to be having like 12. The ones that they do they have us work extra hours because they might be to lazy to hire some new people. It's getting to the point where I am thinking for quiting but I really don't want tot because I absolutely love the people that I work with and i get along with them so well. It also makes me a little mad that i have been asking for a raise for the longest time and they still haven't given it to me. I keep giving them new reasons espeically now that they gave me a new responisibility which is basically to count all the money at the end of the night and do all the banking. So i think i deserve a raise and I am hoping that I get one because if not I might go looking for another job.