Had cold cough for few days it's almost gone ,since yesterday i have been feeling a small shortness of breath it happens mostly when i think about it.

Get examined: Cannot be diagnosed online. See a physician, get a clinical evaluation, diagnosis and treatment.

Heart or lungs?: At your age, a feeling of being short of breath is often due to anxiety. Breathing too fast can make anxiety worse. Another possibility is something decreasing the exchange of oxygen in and carbon dioxide out of lungs. A third cause would be insufficient power in the heart pumping. If the sensation persists, better consult a trained medical practitioner.