Shrimpy, I can totally understand why you're frustrated, but from an outsiders point of view, you have NOTHING to worry about.
If you're sticking to plan, which you are from your diary, then the extra weight this week will defiantly be from your increased activity. I remember when I started serious exercise I sat at 8 and a half stone for almost a month! A MONTH! And in 6 months I'd never always had consistant loses. Your muscles are being used to a greater effect than they ever were before, so they retain water to repair and build themselves. This happens to everyone, but it is scary to see a raise in the scale, but it will settle down and go away. I PROMISE you!