Hi Pee,
I have experienced shortness of breath often, during preg and also when I haven't been pregnant. I was worried it was asthma etc. It turned out to be muscle and back related. My back wa out and then my muscles were seizing up restricting my chest and making ne feel like I couldn't get a full breath, especially when lying down.

This may be totally unrelated to you but I thought I mention it as another avenue to go down if you cant work it out.
Cheers Michelle