Asthma: Given the symptoms of non-productive cough and shortness of breath on exertion, asthma is a strong consideration. The lack of other symptoms such as fever or hemoptysis also points towards asthma. Low vitamin D levels have been associated with an increased risk of asthma.

Anemia: Although the iron percentage is at 32, which is within the normal range for many labs, the mention of iron level warrants consideration of anemia, especially if the patient has other signs or symptoms not mentioned here. However, anemia typically presents with fatigue, pallor, and shortness of breath, which could align with some of the patient's symptoms.
Vitamin D Deficiency: Low vitamin D levels can contribute to a variety of symptoms including muscle weakness, fatigue, and potentially respiratory issues, though it's less directly linked to cough and shortness of breath compared to other options.
Chronic Obstructive Pulmonary Disease (COPD): Although less common in a 22-year-old without a significant smoking history, COPD could be considered, especially if there's an exposure to other lung irritants. However, the age and lack of other symptoms make this less likely.

Pulmonary Embolism: Although the patient does not have typical risk factors or symptoms like chest pain or syncope, pulmonary embolism can present atypically and is a potentially life-threatening condition that must be considered, especially with shortness of breath.
Lung Cancer: Extremely rare in a 22-year-old but could be considered if there's a significant family history or exposure to carcinogens. The lack of other symptoms like weight loss, hemoptysis, or a significant smoking history makes this very unlikely.
Sarcoidosis: An autoimmune disease that can affect the lungs, causing cough and shortness of breath. It's more common in young adults and can be associated with low vitamin D levels due to granulomatous disease affecting vitamin D metabolism.

Cystic Fibrosis: Typically diagnosed in childhood, but mild forms can present later in life. Symptoms would include chronic cough, recurrent infections, and possibly malabsorption leading to low vitamin levels.
Eosinophilic Pneumonia: A rare condition characterized by an accumulation of eosinophils in the lungs, which can cause cough and shortness of breath. It might be associated with asthma or atopic diseases.
Lymphangioleiomyomatosis (LAM): A rare lung disease affecting mostly women of childbearing age, causing cough and shortness of breath due to cystic changes in the lungs.