I went to the Dr. yesterday with a severe pain in my middle back left side when I took a breath, I was slightly lightheaded and felt I had some kind of congestion. He said ex-rays showed my lungs were clear but I was reading low on oxygen. He diagnosed the pain as either muscular or skeletal and sent me home, telling me to come back if it gets worse. It was allready so bad I couldn’t hardly stand it.
On a hunch I stopped off and got some mucinex and doubled up on the dose for about 12 hours. It produced a good hard cough and a clear but very hard mucous came up. Pain went away and lightheadedness cleared up immediately.
I have known several others over the years with a similar complaint who were diagnosed the same way, one lady died. I have to wonder how common this really is.
Weird. I’m a little surprised the doctor sent you on your way when you were hypoxic for no apparent reason. 
If you “just” had a mucus plug obstructing part of the lung that would explain the hypoxia and possibly the X-ray (as far as I understand, the X-rays show places where there’s more fluid e.g. due to pneumonia). I could be wrong about that though.
Yeaaaaaah. That’s a little troubling.
as a doctor told me- there are no nerve endings in your lungs- so you don’t really feel pain - or could be pain in the back or some other muscle-
Could be the pain was from the struggle to breathe (causing muscle stress etc.). Things like pleurisy (which doesn’t sound like what the OP had) are caused by irritation of the tissues surrounding the lungs.
So you may be right about the lungs themselves not feeling pain (I hadn’t known that).