How do you tell if enough is enough?

You ever get the feeling you are doing more than your fare share of work on something only to have it ignored or have to give people credit for something they didn't do? I get that feeling a lot. At work, at school, I feel like I am the only person that cares. Yesterday was truck day at work, which as the name suggests, the semi comes in with parts to restock the store. Usually there are between 1200 and 1500 parts that come in depending on how busy we were two weeks prior when the distribution center counts our sales and writes up the restocking list. Well yesterday was a moderate day as far as parts count. Everyone but 3 people that work at the store were there. I even went in 3 and a half hours early to help out. You would think this would be a good thing. Wrong. The people that were missing were 3 people that actually help me and 3 other employees put up truck. Everyone else just stands around doing nothing. They will find any reason to get out of truck. From going and meeting with commercial accounts to helping customers above and beyond their job description so they don't have to put up parts. Its sickening. A couple of these people are managers that will not do a damn thing unless they absolutely have to. So truck didn't get done, even though me and a couple other guys busted our asses and I came in early. My store manager even came in on his day off to help! How pathetic is that? Same goes for school. Group projects are never a good thing. You get assigned to some random group and you and maybe 1 or 2 others help out. But the slackers certainly come in to finish and get credit! Luckily this semester group members can be fired. Bad news is that means more work for those of us left. But we had to pick up there slack in the first place so that's a moot point. I don't know. I feel like I am doing more than my fare share and not getting anything for it. No thank you, no promotion at work, no nothing. Maybe Ill get a decent grade on my group assignment. That's something... but enough is enough!