I suspect you have strained your illiotibial band (ITB) and the cause may well be the altered position of your foot in relation to the pedal caused by the new inserts. Effectively, the arch supports are forcing your foot to tilt out and downward. I don't think saddle height has much to do with it. In addition, are you a masher or spinner, or as observed by another, have you been pushing high gears uphill (you mention "more powerful" in relation to your pedalstroke)? Pushing harder gears or mashing will exacerbate the problem.