Rheumatoid Arthritis Support Group
Rheumatoid arthritis is a chronic, inflammatory, multisystem, autoimmune disorder. It is a disabling and painful condition which can lead to substantial loss of mobility due to pain and joint destruction. The disease is also systemic in that it often also affects many extra-articular tissues throughout the body including the skin, blood vessels, heart, lungs, and...

Best of Luck.
PS I take mtx and had side effects in the beginning like nausea that I do not have now.
My drug fact sheet lists lung damage under less common side effects. It includes cough, shortness of breath and/or fever.
Hopefully it's nothing but you should call your doctor to be sure.
I hope you feel better soon. :-)
Lung issues are a big deal on MTX. I had a problem with pneumonia a couple of years ago and now I have to go every year to a pulmonary doc to be checked. If your doc doesn't like it--oh, well. Find another doc, but to me, we are all ultimately responsible for our own issues. I research everything. I know my "Big Picture" better than any one.