How much is to much

My job has been crazy for several months now, with all the extra hours of training, plus full time work,no manager and so on, I had hoped that things would begin to get better now that we have a new manager (he started two days ago) now I am not sure.
My old manager (who is still our GM and company trainer) approached me awhile back and told me once things settled down I could have FRI,SAT,SUN MON off, I will not work the am shift anymore as it starts at 5am and that left my kids to get up and off to school on their own, so I was told I could have all my hours in the afternoon and evening and would be guaranteed between 28 and 30 hours per week, this was perfect for me. He had me put a schedule together based on every ones availability, well another girl who works with me had been doing a temporary schedule and I heard her having a "fit" because I would not be working weekends anymore. So to condense the story she took it upon herself to make up a different scheduale and give it to the new manager and then told me he did not like the one Tyler and I had done and could I look at this one and make sure my days and hours would work. I almost had a heart attack she had me off Sat and Tues, working all the rest of the days split shifts two of which were am shifts and my total hours were 16.5 for the week...now I live 20 min away from the airport for me to drive back and forth twice a day for a 1 to 3 hour shift would in no way be even remotely profitable for me. Well I told her there was no way I was working that and if that was what they wanted they could consider this my notice. Tyler happened to be there and so he talked to me, re enforced that he had said I could have the schedule he had offered me, I was not to leave the kids to work a early am shift without being given notice and a choice (so I could make arrangements for kids) and he would talk to the new manager, turns out the new guy had never seen the schedule Tyler and I did, he did go over what I wanted and I agreed to work either Friday or Monday if I had the other three days off, so I felt pretty good about that until he made a comment in passing to me, he said he was bringing some employees from his old airport in to fill some of our open positions, this is great I think but then he said right now I am catering to people because I need them, but when my new people get here some people may quit because I am not going to give them the "good shifts" while my new people work whatever is left. So I guess time will tell what happens with my shifts. On top of that I hurt my back last week at work, a bag got stuck on the belt as I was pulling it into the cargo bin so I have been at the Dr and having some real problems with it healing, so that is not helping.
I feel like I have put up with to much at work the last few monthes (far more than I want to get into now) so I am leary to just give up now, but I do wonder how much is to much, and is it worth it when I no longer enjoy going to work?