OP here, back with an update.

I had my DH massage the frozen shoulder, back and neck on the affected side daily for a week or so. He really worked at it for 20-30 minutes a night. It loosened gradually and my range of motion improved. i was pretty surprised because the occasional professional massage had not done much.

For Christmas, I received a heated electric mattress pad which I have been turning on HOT. I climb in bed and it is like a sauna. I turn it down to sleep, but still really sleep with it fairly warm through the night. It has been 6 weeks and I wake up not stiff anymore.

I guess, from my little experience, the massaging daily, plus the heat have really helped.

FWIW

I started seeing a chiropractor about a month ago. It is costing me a mint, as we have a high deductible, but I think he's done wonders for me. He took an xray and showed me some disc degeneration in my neck, but he feels confident that with exercise and lifestyle changes I can stop it from progressing. He has adjusted me several times. In a month, the neck pain and stiffness has almost disappeared; I haven't taken a pain med since I started with him, and my shoulder has improved a lot too. I don't know if the result is more because of the adjustments or because of the exercises he has me doing. I am strengthening the muscles that support the spine and shoulder. I am cautiously optimistic that I may be able to get back to swimming by the new year.
By the way, he told me that yoga is great for people with healthy spines, but he recommended that I lay off it for now, except gentle yoga. This made me sad, but I'm hoping he oks me going back once I'm completely pain free.

I just had frozen shoulder + cervicalgia. I went to an orthopedist who put me on a 6 week physical therapy regimen. Just had my last PT appt. last night and I am basically cured.. have to keep up on my neck/shoulder strengthening exercises but otherwise am pain-free and have not had a headache/migraine since starting the PT.

You may also want to try a chiropractor.

I agree about the yoga. People, especially women, tend to hold a lot of tension in their necks/shoulder areas. You really have to be mindful of your body and when/where you're tensing. If your shoulders/upper back are constantly contracted, you will experience constant stiffness. Try a more rigorous form of yoga though (power/Baptiste, Bikram, etc.)

So, it sounds like a "frozen shoulder." It is worse on one side. I am wondering if any of you have experienced this?

I will be going to my doctor, and will post back here.

But I'd like to hear from someone who has had this.

Yeah I would see a doctor this week. After you have been seen try yoga at least weekly if not daily. I also get these type of comments and only yoga helps keep me from being so stiff.
Plus google frozen shoulder

Go to a doctor! Seriously, why are you asking strangers on the internet. You are having symptoms that are getting worse. Go to a doctor.

I am a mid- forties woman. I have been experiencing a stiff upper back and shoulder area for months. It is very gradually getting worse, and I am no longer able to raise one arm comfortably above my head. It feels like it is frozen and immovable. The back of my neck aches. I have tried massage and that has not provided any real relief. The massage therapists consistently state how tight my shoulders, back, neck, and upper arms are. If I could describe this in any way, it feels like I am slowly "hardening" and losing mobility. I am wondering if anyone else has experienced this.

I also am fatigued a bit.

Any thoughts or suggestions?