Are you actually breathless, or is it that you are not getting enough oxygen? Also, is your breathing worse when you are outside as opposed to indoors?
If so, you might have whatever I have, which remains a mystery. I have had a battery of tests and my heart and lungs are both mechanically fine, but I desaturate as soon as I walk outside. It's very debilitating and has led to my putting on weight and restricting my activities.
I do take Lansoprasole, but this was prescribed a while after the breathing issues started, so I don't think there is a link in my case.