First day of orthotics: is back pain normal? Can I work out?

Hi all. I'm trying a different orth for my light pronating and flat feets. Last year, I tried, for some months, a little ort that had not an important arch support. Today I start using an orthotic with a good arch support. I'm experiencing a little bit of back pain. I wore them for 2.30h. Can I go to the Gym with this back pain, and without using them when exercising until I adapt to them? I have a little knees condropathy, and they are it seems orts are not causing pain there. Only in back pain. Thanks!

Sorry my eng