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Those defeats sandwiched a convincing 27-6 victory over France at the Millennium Stadium, and North has urged his teammates to rediscover the form that saw them dominate the Championship for the past two years.
"We have got to make sure we are consistently performing rather than having these ups and downs," said North, who won his 39th cap for Wales at Twickenham.
"It's continuity, we should really be performing week in and week out, but at the moment we are bit up and down. It is massively disappointing.
"Emotionally it's not like we weren't there - the emotions were good - I think we have just got to step up to that pace straight away.
"We knew England were the team to beat right now, they are the form team, and they showed it. They showed a good variation in their game and in the end we were out performed."
And North highlighted the first ten minutes of the game, during which Danny Care notched England's first try from a quickly taken tap penalty, as one of the key reasons Wales are out of the running for a record third title next weekend.
"As a team it is all about getting into the game," he added. "In the first ten minutes they came at us really hard. We knew they were going to but we didn't really ride the wave."