What Causes Shortness Of Breath Apart From Low Oxygen Levels?

OK im just about fed up I ve been going to the ER and doctors office since sunday may 15, 2016 for my breathing I ve been having shortness of breath at night during the day. It s like harder to exhale than inhale and everywhere I go they say that my lungs are clear and my oxygen level is like 98% but i m still having shortness of breath I have been taking breathing treatments day in and day out and that s like the only thing that seems to give me relief but it only last for about an hour and then im back where I started. I don t know what s going on but it is very scary everybody thinking im crazy because I keep saying im shortness of breath meanwhile my oxygen level is high. Everytime I go somewhere they don t give me no type of injection or medicine the only given me over the counter drugs. Now I have anxiety really bad especially now since everything i m doing not working. I take Montelkast/singulair Cetirizine/zertec and advair every night and I also do the Flonase but these problems are still here i m not wheezing until I eat something. Somebody please help me no one believing me and im in this all alone. Mind you that its now may 20, 2016