If it helps at all, I have dealt with this several times in this pregnancy....and I hadn't even used my inhaler in years beforehand. Seems it was irritated by allergens (we moved, so it has been dust central) and then the chest cold I currently have. It is scary, I know, but I found that the more I worried about it, the worse it got. (go figure-- of course the stress further constricts your breathing). Go see your GP. Likely they will do some breathing tests to help determine the extent of the problem. I did find that a warm shower and hot tea help me at least counteract allergens and slow down a little...
might be viral too...elderberry, perhaps?
Hang in there. It will get better!