Im not that far along, but since u have no comments my opinion is that ur baby is probably tucked against ur lungs or has its little foot shoved up there.
Im 38wks as well n sometimes its hard for me to breathe because she hasnt dropped yet n all my organs are smushed together somedays are better than others with how she is positioned n i get awful backpains somedays too ima ftm so idk if what ur goin thru is a sign that labor is near hth
My baby has been dropped since 33 weeks