it often averages out over a month. I would say to begin with on the first few steps you can loose a stone a month. Key is to make sure you are drinking all the water.
Its horrid when weight lose is soo low after all that effort. but it does work, there can be loads of reasons for a low loss week, like time of the month as well.
2lb is still a good loss and it is going the right way. Also are you getting measured as well? you may find you have lost a full inch or two of your leg or arm or waist.
Good luck for your next weigh in.