It could be something you are consuming.
I had the same symptoms for two years. I had lung tests and all was ok according to the doctors. Others kept telling me I was having anxiety or panic attacks.
I was constantly out of breath and hyperventilating. Some days I'd hyperventilate all day and most of the night.
Yesterday I decided to go without my usual morning coffee and since then all, yes 'all', the symptoms have completely disappeared.
I'm not saying this will work but go without something you usually eat or drink for a couple of days such as in my case it was coffee. It might even be something that is supposed to be healthy but just try a different tihng every couple of days.