Hi everyone - I have found this thread really useful, going through this myself at the moment, so I thought I'd make an account and contribute my experience.
I'm also a female, age 43. For a few years now, I've experienced what I thought was a 'shoulder flare-up': For no reason that I could fathom, once every 4-6 months or so, all the muscles in my left shoulder just seemed to spasm for many seconds. When that faded, I was left with a strong dull ache just off my left shoulder blade. This would take about 7-10 days to fade. During the day, the pain wasn't too bad. At night it was really horrible, especially for the first few days. I saw a reputable acupuncturist for many weekly sessions, without any long-term improvement (in terms of reducing the incidence of this). At this point, I just thought it was some muscular thing to do with my shoulder. I didn't notice any muscle weakness.
About 2 weeks ago, I felt a slight discomfort in the usual place and thought to myself 'I hope I'm not getting that shoulder thing again'. I then did a home yoga class, which involved a lot of Downward Dog. They emphasised the importance of getting a straight line from hands to butt - even if bending at the knees. So there was a lot of upwards pressure from my shoulders. I didn't notice any injury or event during the class and finished it as usual. After the class, sitting at my computer, the pain just started to come on and got stronger and stronger until I was in agony.
My entire shoulder hurt - the shoulder blade, across the top of the shoulder, down the top of the arm, and in front where it connects to the collar bone. (That bit hurt especially, even water from the shower touching it, hurt.) I took ibuprofen, acetaminophen, put Deep Heat on it and tried to go to bed. But I couldn't sleep due to the pain and was awake all night. The meds did nothing for the pain that I could tell, neither did naproxen when I tried that.
The next day, I felt slightly better so I decided to try rest and meds and a heat pack for a few days before going to the doctor. The days were not too bad, although my left arm was pretty useless - it had no strength or power to reach out and I kept the elbow tight to my side and tried not to use it. I couldn't even touch my face or pick up my toothbrush. The nights were very painful. They got even more painful when I then pulled a muscle in my right hip by trying to turn onto my side without using my shoulders to rotate (because that hurt) - it felt like my leg was going to pop off. I just felt like my body was falling apart. I stopped using any meds because none of them worked. I can only sleep on my back now, as I can't turn onto my side due to my hip.
A week after the injury, I went to my doctor. He took some bloods for auto-immune issues and joint disorders (I think because I messed my hip up too - but it's just to be sure) and we're waiting for results. He asked me to do various moves and said I have full range of motion in my shoulder (even if it hurts a bit to move it) and I could resist him when he asked me to and pressed on my arm in various ways. So he said he doesn't think it's my shoulder.
I made an appointment with a physio who is a shoulder specialist. He was great and did a lot of tests and really listened. There was one test he did with my left arm where he held the arm bent in a certain way with me lying down and bent the wrist in one direction - which didn't hurt at all - and then he bent the wrist the other way, which did hurt the shoulder. He said that test was an indication it is in my neck, because he had moved nothing in the shoulder joint whatsoever - he'd only bent my wrist differently. Which somehow indicates the neck?!? He said he thought it was cervical radiculopathy coming from my C6 or C7 joint in my neck.
He gave me some exercises to do which sound like some of the McKenzie exercises here - looking down so my chin touches my chest. Looking right and left. Tilting ear towards shoulder on each side. He said I should stand tall always, use my full height, draw up through my skull. (He didn't actually explain how any of this was supposed to help, it was only when I came home and googled it and found this thread, that I realised we were trying to take pressure off the nerve.)
He also had me kinda polish a table with my left arm, moving it in circles - and if possible do that on a wall as well, like you are polishing a wall or car. And he had me hold this lightweight stick up over my head in both hands at the same time. This was hard work and there were a few twinges but it wasn't too painful. The takeaway points seemed to be that there is nothing functionally wrong with my shoulder muscles and I have to try to use my arm even if it feels like it takes a lot of effort. (I don't know if he was worried I was going to get frozen shoulder or something through not using it.)
So that was 5 days ago and I've been doing my exercises many times a day. I am mostly pain-free now (with the shoulder, at least!). Although there are often twinges and aches which come and go. But it's a big change from constant pain and just a few breaks in the pain, to now mostly no pain with occasional twinges.
But the shoulder still is incredibly weak. When I do my table-polishing thing or use my arm, I feel like I've been working out and pressing weights when all I've done is pick up a pencil on my desk and put it back down again. It's so exhausting, I feel like I need a little nap after reaching out for a pencil. Which is ridiculous. And I'm left-handed as well. Still, I'll take weakness over pain any day...
I am probably going to ask for an MRI, just because this has happened to a lesser degree several times in the past and it seems to be happening more frequently. And obviously worse. I'm also now afraid to do yoga again or lift things over my head, for fear of causing this again.
I hope you all get better soon!