Biceps and deltoids hurt after position change

My bike fitter (FIST certified) dropped my handle bars about 3 cm. It felt great in the shop. After going for my first ride, though, my posterior deltoids and biceps hurt after about 5 minutes in the aero position. I have always been able to hold the position for hours at a time without any problems with my arms/shoulders. Yesterday, 5 minutes tops.

I assuming it is related to my position change as these muscles didn’t hurt before the ride.

Is this a common occurrence, and I just need to fight though the pain, as ultimately I will be accustomed to the new position, or have I gone to to severe of an angle?

(I guess its possible that the position of my hands is the real culprit.)

Any comments?