Moving the cleats forward mean you might have to push more with your toes, because they aren't under to behind the ball of the foot. There's also a shorter reach to the pedal if you left your seat where it was. If it made you point your toes down, then the constant shortening of the achilles (and the different strain on the calf) might be your culprit.

Have you looked at some of the cleat placement information on the cyclingnews.com website? I find it really useful. It helped me ward off some peroneal tendinitis. When you change your cleats, though, you might also need to change your seat.