07 weight loss battle-7 weeks in

Can someone please tell me how in the heck the scale said that I gained 5 pounds this last week? I didn't eat much different than before and it said that I gained 5 pounds which is discouraging seeing as how I went to the gym 3 times last week, biked 14 miles on Friday and raked leaves all day Saturday. It doesn't make sense. Oh well, I suppose it could be "muscle" but I want my numbers going DOWN not up! Oh well I've got this week to get the number back down before next Monday's judgement day so I gotta work hard this week!