I really appreciate your suggestions!

I don't have a picture of me riding, but when I go back to the LBS I'll bring my camera. I'm 50 years old. I don't carry stress in my shoulders or get headaches, fortunately.

Triskeliongirl - I will try the wider handlebars, thanks for the information. I think he said my shoulders are 39 cm wide. He did say that he moved the seat forward to get my knee over the pedals.

I suspect my position could use tweaking. I have been doing some core strengthening exercises all along. I've read about using the stomach and low back muscles more in cycling, but honestly I don't know if I do this or not. I have considered finding a physical therapist who is knowledgeable about cycling. I'm sure there are a few in the Bay Area, and I don't mind seeing my doc.

And glasses - yes, Ducks! I got a special pair so I wouldn't have to tilt my head up to see the screen. I sit in front of the computer all day at work.

I did ride a 51cm frame early on, and felt way too stretched out. I had those pains in my lower neck immediately. I told the sales guy this, and he didn't seem really engaged in the issue. That made me go to other stores, and this one in SF suggested I needed a smaller frame. Their "bike fit" guy has been very patient, so I'll see it through. But - I have considered trying other bikes.