That is because you are exercising heavily. You're using up the energy supplied by the packs for day to day living. If you want to continue, you'll need to replace your exercise calories somehow, without carbing up.
I've been doing vlcds for 5 years, with varying degrees of success. I've done it perfectly for 7 months (inc RTM) and I've made every mistake in the book over that 5 years. One absolute contact for me, and everyone I've seen do it personally (off forum I mean) was that if they exercised too hard, or if they exercised too soon (first 2 weeks), they lost less short term.
Whenever I did Slimming world, I saw that every time someone started exercise, they lost nothing that week, but lost a lot a week or two on. We don't get our rewards the week we do these things - just as we often dont get our punishments till the week after either!
Good luck and stick in there - it DOES work for you, but you'll have to consider some other compromises I'm afraid - like easing off the exercise!