I know this might sound daft.. but could you be tense?

Whenyou tense your muscles become stiff...
If its a new bike, and a new riding position it is possible that your are not relaxing your shoulders and back when riding.

My advice would be to take some deep breaths, shrug your shoulders and make a few neck movements and settle.
Go into the corners with your shoulders dropped and turn your head to face the direction you are going...

Dont know if it will help, but its worth a try.