I was running some Google Adwords campaigns and my minimum bid was around 50 cents. I stopped these campaigns for a few weeks. When I restarted the same campaigns with the same keywords a couple of days ago, the minimum bid for most of the keywords jumped to $10.

The only explanation on the Adwords help info is that the quality score for my ad, keywords, and/or landing page is low... but how can the quality score diminish so much in a few weeks?

Does anyone know if Google changed their Adwords criteria recently? Has anyone experienced something similar?

Thanks!