Don't get discouraged! You are doing great. It is completely normal for the body to lose weight in chunks. It would be nice if it were a steady curve downward, but it rarely works like that!
There are so many things that could be going on here. Some people are sensitive to caffeine and need to cut it out to lose weight, some people get stalled when they eat processed foods like shakes, sometimes it is just that it is a point in the monthly cycle where the body grabs water. Keep experimenting, see if you can tweak something to make your body burn fat better. Listen to what your body is telling you. Do you have energy? Do you need to eat more? If you are going low carb, make sure you get plenty of fat and adequate protein. Exercise will benefit no matter whether it helps get over this stall or not. Don't even think about getting concerned until you are at the same weight for 4 weeks, though. If you do go that long without any movement in weight or inces, you just need to figure out what you need to adjust. This gives you a chance to know your own body better, and that is a good thing. Keep up the good work!
Theresa