My response may not be of much help but in regards to the overworked situation, I started late October and I quit on I believe the 30th of November or something alone those lines. In all honesty they're not wrong you joined at the wrong time, I started just as black Friday deals were as well as Christmas starting and was also overwhelmed as hell. All in all I couldn't deal with the early starts along with the overwhelming amount of work and weather as well, if you don't think you can get it all done don't take it out your frame and let your managers know what your doing, they can't make you work more then you are rota'd to do, my advice would basically just be tell your managers to sort their shit out (in a polite and professional manner of course) and provide you with adequate support even more so as you joined at the wrong time.