Hi Laura,
I had exactly the same when I started exercising - I was going to the gym 3 times a week, eating bang on plan and generally doing everything right, but my weight loss tailed right off. I went from losing 2-3lb a week to losing 1lb, 0.5lb, STS ... I was really disheartened, and it just made me want to not bother with either. Lots of people I spoke to offered conflicting advice - some said it might be muscle gain, others said this was a myth and highly unlikely to be the cause ... In the end I did stick at it, largely as a lengthy chat with my other half reminded me that part of me wanting to lose weight was for health reasons, and that I shouldn't get to blinded by the figures on the scales as these don't actually mean anything. After all, I'd take staying at my current weight if I could miraculously get into a size 10!! I took my measurements and tried to focus on the way my clothes fit, as I was still losing inches even when my weight loss figures at weigh in seemed to wain, but I know it's hard.
I think I've now found a bit of balance - I still go to the gym but have dropped to twice a week. I also don't go in the 48 hours before weigh in. (Lots of things I read suggested that your muscles retain water after a workout - no idea how long this lasts, or if this is the reason why it works for me, but it has produced slightly more pleasing results at weigh in since I've adopted this tactic!) I'm still losing pounds as well as inches, so am happy overall. Guess the only advice I can give is therefore to refocus your goals, try not to be disheartened (hard as I know it is), stick with it and - if you like - try giving the gym a miss for the day or two before your weigh ins.
HTH and well done on your loss so far!!
but it's my own fault, was eating ALOT of junk EVERY night for 3 weeks 
