m.s. & breathing difficulty…?

I have multiple sclerosis & I have to wonder if my breathing difficulty is a result. I’ve never really known why I have trouble breathing sometimes. But I have heard that ms can cause this. I could have asthma, but it seems unlikely (I think- not sure, don’t know much about asthma), because this is a subtle thing- no attack of extreme shortness of breath ever. Also, I never experience any anxiety with the shortness of breath, so its not an anxiety attack. anyone know anything about the following…?

-harder to breathe at night when I’m sleepy, or when I’m laying down.
-not a dramatic "attack" of it, just cant seem to get quite enough oxygen when I breathe in sometimes.
-some days I just feel like all day I am fatigued by my lower intake of oxygen- varies day to day.
-on the days I experience the previous symptom, I also feel stiff in the muscles in my chest & back (near my lungs)
-somewhat lightheaded when I exercise, even though I’m in shape & exercise regularly.

If anyone has any thoughts on this at all, I’d like to hear it, thanks!