I have similar symptoms to yourself with normal blood oxygen levels, etc, but extreme shortness of breath. After finally receiving appropriate medical investigations, including vq scans and pulmonary function tests (including the 6 minute walk test), I have finally had my condition diagnosed as chronic thromboembolic pulmonary hypertension. The walk test had to be cancelled half way through as it drove my heart rate up to dangerous levels. Vq scans will show movement of blood and air in the lungs, in my case showing patterns of blockage of blood vessels.