The equivalency factor for the purposes of tapering is sometimes too high or too low due to our differing physiologies. It's possible you don't need to be on this amount of valium. Another possibility is that valium just doesn't agree with you. This happens occasionally.
It would be reasonable to begin tapering now. You can actually cut up to 3mg valium at this point since that would equate to less than a 10% cut. But to play it safe, I would suggest a 2mg cut, every 10 days. 7 days isn't quite enough time, IMO, as valium is long acting. Give that a try.