It IS maddening isn't it. But, I gotta tell you, expect more of the same. You had an amazing loss, and now the scale went up. This was very normal for me - particularly if I was exercising intensely.
It could very well be water weight. The scale WILL go up and down within a 5 lb range even when you are perfectly on plan.
Like Colleen, I need to weigh myself daily. But I am a data geek so I put everything into Excel. I tracked "averages" by the week, two weeks, month, and two months. When my daily weight went up, I could look at the averages and see that my weight was actually going down - that it was just a "blip" for that day (or even couple of days or week).
If you don't like excel, I bought a scale that keeps the weights for 4 people, and gives you today's weight and compares it to yesterday, last week, last month, and 3 months ago - it is really a wonderful thing
So - stop, breath, relax and realize that you are normal. Stick to your plan and those pesky lbs. will disappear soon.