Mid-week rant

I feel utterly miserable at work. I'm into my sixth month already but I just cannot cope. Suddenly, everything is due on the same date and I just don't know how to do anything at all. I feel like everything that's asked of me is an impossible task. This stinking job here is way beyond my threshold for the unknown. I'll rate it as 10% known, 90% unknown. Now, can someone just tell me how am I supposed to do my work if I don't know how to do 90% of it? Why the heck did I even get hired? Oh, I remember now: to replace the employee who left on short notice after working here for about 5 months only. She probaby couldn't handle all this endless shit hurled at her. And now I'm afraid that I too am facing the exact same situation. I really ought to have just resigned last month to save myself from drowning in all this mess.