a callous on the pinkytoe side of things suggests to me that your orthotics are making you over supinate, unless you've always been an oversupinator. Or that you are wearing curved-last shoes when you should be wearing straight-last shoes (which is more likely).

But I'd really need to see you walk and look at your whole foot/ankle/leg to know what is going on.

There's a really cool series of pictures used by Gary Gray PT, that show callousses and what they indicate. Cool stuff. It's gotta be on the internet somewhere!

Have you asked your orthotist why you are getting callousses? Did the orthotist get to look at your shoes as well?