That's almost 9 pounds in 3 weeks. Are you sure that you haven't changed your eating habits at all? What about medications? Honestly that's they only way that I could see you gaining weight, unless at the same time you developed a medical issue.
I'm sure someone will tell you (if they haven't yet) that muscle weighs more than fat, it doesn't, besides gaining 9 pounds of muscle in 3 weeks is impossible.
IMO either you are eating more and don't realize it or your sodium intake has dramatically increased.