Dreading going to work

I haven't dreaded work ever before; it's a new thing for me. I used to dread going to school so I remember the feelings. I used to get so worked up that mum would assume I was ill and keep me home, which at least kept it at bay for a couple of days. But I can't phone in sick today, I've been in a new job (at the same workplace) for less than a week. I can't afford to lose face.

But the truth is I'm not enjoying it any more. My role is to keep the displays neat, but there's so much time between my shifts (I only work 6 hours a day, not always when we're open, and the shop is open for 10.5 hours) that it's always a mess by the time I get back. I know I'm not the only one feeling the pressure but I get a lot of the heat from the shop manager, who expects me to have instant knowledge of the new department and new role and I'm finding it too hard. Not to mention that I'm working with people I hardly know. One of my new colleagues, in particular, is very difficult. She frequently follows me around (when the shop manager is having a go at someone else for once) and tells me the displays look "shit" or rebuilds something I spent hours on just as soon as my back is turned. Already I've spent more time than I should crying in the back room, I can't go on like this.