Overtime forced on me

I'm so frustrated today and want to quit my job so bad. They announced today that we have to work overtime... 2 hrs per day and 3 hrs on a stat holiday (monday where I am) for the next week to get our work done by deadline. The reason its not done now is because the client hasn't been holding up their end of the bargain and we haven't had what we needed to get the job done quickly. Its a big international company I work for so there is no talking to management to sort this out, we've stated our grievances and been told its just the nature of the work. My father just passed away 6 days ago, I'm already suffering depression and anxiety and I hate my job... now I have to do more of it. I just want to throw in the towel and tell them to take there job and shove it! But I have a daughter and grandson to support :( I'm at bf's at least so its a bit better than being at home. I can work from here but he is working evenings so I wont' see him much the  next couple days. I'm just tired and wore out and I want out... its one of those 'stop the world and let me off' days... its just too much for me to take. March and a southern vacation can't come fast enough. And I will be working very hard on my bookstore plans once I have time again. With this overtime I can't even think about it. I'm on a break now and have to work later this evening for another 2 hrs... #$%$!$  I hate my job!!!!!