What are the causes of asthma? Can GERD contribute to? I'm often short of breathe.

Multiple. There are several possible causes of asthma symptoms, including infection, allergy, and exercise. Gastroesophageal reflux disease (gerd) can certainly trigger asthma symptoms as well.
See below. Pneumonia undertreated infections and scarring smoking or occupational exposure gerd can also contribute to asthma see pulm doc for treatment including Flovent or asmanax.

Related Questions

Dry persistent cough. Negative for allergies, gerd, asthmas, cancer & heart conditions. Leads to shortness of breath. What can I do?

See physician. There are so many causes that you excluded so you should see your physician for proper evaluation.
Consider bronch. On occasion recurrent dry cough with associated shortness of breath, especially if the difficulty breathing is on inspiration, can be related to vocal cord dysfunction. This may require an ENT physician to directly visualize the larynx and below. If that is normal, a pulmonologist may need to look directly into the lung for the cause.

Shortness of breath with mucus for a year. Doc has said Gerd. Doesn't think asthma. Smoked 10 yrs.25. Lung test normal. Copd? Pneumonia? Just smoking?

Consult an allergist. There are many causes for breathing difficulties and I think you are too young to have chronic bronchitis from smoking. If you have problem getting enough air when breathing in, conditions such as vocal cord dysfunction needs be ruled out as well. You should definitely stop smoking however regardless what is causing the breathing issue.
Quit smoking. The most obvious answer of course is that you have to stop smoking. There is no benefit from smoking, and as long as you continue to do so, you will be short of breath and have increased mucous and cough. You know this. Smoking makes asthma, GERD and COPD worse if you have them. Smoking causes other serious chronic health problems, such as cancers, stroke, heart disease. Have you tried Chantix?