Problems breathing when exercising - asthma?

Dear Ask The Doctor: I exercise regularly and have a healthy diet. I am about 5'9 and 155 pounds and in decent shape. I've taken a test before that says my lung capacity is above average. However, I noticed that when I do cardiovascular activities I often have trouble breathing, even when I'm not exerting myself that much. I feel like this is a pretty big problem because even though I have been exercising regularly and conditioning for sports, my ability to breathe while running for long periods of time has still not improved noticeably. Even though I can keep up with just about everyone else I work out with, I feel very out of breathe after doing running exercises, when most of the other people seem fine. I experience no chest pain. I also have a deviated septum and a family history of sinus problems, and minor lung problems (nothing dangerous), if those have anything to do with my problem. I can't for the life of me figure out what the deal is. I toyed with the idea of it being asthma but I don't get any problems at all except for when I run for a long time. The easiest answer I can think of is that I'm just out of shape, but after having done this for awhile, I feel like I should be improving. Please let me know what the problem might be and what I can do to improve it.

Dear Erik: In my opinion the deviated nasal could be the reason for troubled breathing. Since deviated septum cause decreased nasal airflow, you may feel out of breath at times when your demand for air or oxygen is increased, which may not be felt in normal day to day activities. You may consult an ENT specialist for the clinical examination of the degree of deviation of the septum, the condition of the sinuses and the options for the treatment. Surgical correction of the deviation of the septum, called septoplasty, is the recommended option for the long term cure.