Pushing a 53/12 in the flats isn't exactly easy... I don't whip out my 53/11 unless I'm descending. That doesn't make you a weak cyclist.

I would recommend picking up a cyclocomputer with a cadence function, and focus on keeping your cadence around 80-90 rpm. I think you're just burning your legs out turning a much higher gear than you need to. Focusing on your cadence will help keep you in a more efficient gear.

DrPete