Anxiety and depression can be a pain in the neck, back, and pretty much everywhere, literally. I suffer from chronic muscle tension, and muscle knots. Flare ups can be quite bad, and last for weeks, months, but I do get some relief. I do not take meds, but my Dr. assured me NOTHING was wrong with me, when I was REALLY hurting last year. To the point where I could barely do much. I focused on the muscle knots and pain so much, it made my anxiety worse. My knots got so bad at one point, that it made my muscles feel super weak at times, sometimes my arms would shake. Very scary, but my Dr. reassured me, that nothing was wrong with me besides anxiety and muscle tension. You don't even have to be super anxious to have muscle tension if you have GAD. Hope this helps!
While anxiety can be the cause of this, anxiety sufferers are not immune from physiological problems everyone gets. I think you posted before, and my own belief is you're probably just recovering from the pneumonia, which is a very severe illness. For all you know, you're still sick with a virus or infection the doctors haven't correctly diagnosed. Yes, it can be anxiety, but it can also be something else. I suffer constant pain, but I'm in my Sixties, but part of it is from anxiety and part of it is from actual physical problems. What the anxiety does is make the neurological system more sensitive. I wouldn't expect this from someone your age.