Hey Katy, don't beat yourself up over those 3lbs. I am a daily weigher just because he helps to keep me accountable so don't think I am a good girl when it comes to the scales, but when it comes to SW try to stick to the once per week weigh in.
As for your body, you are a machine when it comes to exercise and I am very jealous hehe but if you at strict with yourself and consume a sudden high intake of calories your body will go into a bit of a shock and think wooooo she is finally feeding us, quick hold on to it! I think it's called glycogen that is stored?
Anyways I'm sure it will come off just as quickly as it came on and with all the exercise you're doing try and up your food intake, even of its just an extra chicken breast or a massive salad.
I know I'm much bigger than you so you might not trust what I'm saying but I promise it will work!
Kate x