Ill jump on this thread...

I just started on a road bike this past weekend too but am not new to riding. I was fitted to the bike as well, its a new bent over riding position (obviously) and Ive started wearing a helmet.

When I was on it Sunday night, I did prob 8-10 miles when typically I would do about 17+ on my other bike. Im easing into the new ride position cuz like was mentioned...I know i'm tense. Ive had some neck/shoulder ache afterwards just like the OP. Most likely from having that extra weight on my melon and not relaxing enough during the ride.
I expect it to get better. I ride about 3 times a week...