Yup. We always warn our patients that when they begin to use their new orthotics suddenly the muscles are working in a new (better) functional postion. They will get tired.
You are retraining muscles and muscle firing patterns.
We have our patients return in 2 to 3 weeks for final adjustments to their orthotics, if needed. It takes about a week just to "break in" the orthotics adding an hour a day, then a couple weeks to adjust to the new functional position.
If you are in pain (as opposed to just being tired/sore like after a work out), please call your orthotist so they can see how the orthotics are doing with you.
"If Americans want to live the American Dream, they should go to Denmark." - Richard Wilkinson