OK - first, breathe.
Your weight is going to fluctuate day to day regardless of whether you exercise or not. What you want to see on the scale are downward trends over more than just one day's time. That's why we all say DO NOT WEIGH IN BETWEEN YOUR WEEKLY WEIGH IN. If you are at ALL emotionally attached to what the scale says, save yourself the stress and just don't do it.
That said, you may need to reduce the intensity of your workouts. Look at it this way - if you exercise for 45 minutes on the elliptical, and burn 400 calories, that is more than HALF of your entire daily intake. You would have to have FOUR extra packets to make up for the calories you burned, and you NEED to replace what you burn because your body needs fuel for muscle recovery. One packet isn't going to cut it. Also, as was mentioned, your muscles retain water when they are repairing - and if your muscles are sore, they are repairing.
There's nothing you can "do" to counteract it - your muscles have to go through their process, you can just make sure you drink PLENTY of water so that when your muscles are not retaining it anymore it flushes out.
You may also want to have a heart-to-heart with your coach - if you truly feel you NEED the exercise, and are willing to take lower losses (that is the trade off when you are on IP), work with your coach on a plan that you both can live with. And then follow it