I feel breathless even when my oxygen level are at 98 or 97 on the oximeter, what may be the causes?

Reason for oximeter?: Normal healthy people usually don't have a pulse oximeter (unless they are pilots, etc...). There can be many reasons for shortness of breath, unrelated to the reading on an oximeter. For example, if a person is very anemic, her pulse oximeter reads normally even though she can be very weak from anemia. Other heart and lung problems can happen, even with normal oximeter readings.

Many possibilities: %oxygen saturation doesn't correlate well to a person's degree of breathlessness or its causes. Shortness of breath or "dyspnea" can be due to lung, heart, kidney, or blood cell problems. It is commonly caused as well by lack of stamina and conditioning such as in patients who live very sedentary lifestyles. Of course, smoking is a huge risk factor. You need good physical examination.