What did I do?

Ugh. I stepped on the scale yesterday instead of waiting until my normal weigh in day. It was there, I was there, it just kind of happened. And then I wished it didn't happen. Isn't that the way it goes. It showed me being 3 pounds up but I know that can't be right, can it? I've been watching my calories and have been under all week AND I've been exercising. So I know that it is something else. Something like the whole muscle weight vs. fat weight thing (even though I've read that it isn't true) and I don't really think I have put on muscle. I've been doing push ups and walking not any weight lifting. I have not been great with my water intake and I am a salt fiend so I'm thinking its water retention. Thats what I'm going with for now anyway. and I guess we'll see how it goes when weigh-in day gets here.