Of course you should first ask your doc. As for my opinion, you'll probably be ok for now since you're just 4 months along. As you progress though you should listen to your body and if its possible quit when you feel that its getting to be too much. I worked at Disneyland throughout my first pregnancy. I had to stand for 8 hours a day, mostly in a row except for my half hour lunch. It was soooooooo hard on my body. I sometimes cried at night because everything hurt so bad (feet, back, you name it). The doctor told me it was fine but I sure didn't feel fine. If you stay, your last trimester will probably be rough. Do you work 8 hour shifts or 4? That might make a world of difference. Don't push yourself, now's the time to relax and take care of you if you can.
Lots of luck!