Are you riding clipless pedals on the Madone? If you haven't done it yet, you may want to research a bit about q-factors and, if you are using clipless pedals, cleat rotation. I say this because it may be that the beach cruiser bike you have has a wider q-factor (essentially, space between the two pedals) and platform pedals and all of that allows your foot to be in a position that doesn't cause you as much pain. Fortunately, q-factor and cleats can all be adjusted.

You are doing the right thing by not pushing it until you figure out what is causing the issue. Don't want to make things worse!