Pain in the left eye lasting for 15 days can happen for several reasons, including eye strain, dryness, sinus pressure, allergy, migraine, nerve irritation, infection, or inflammation inside the eye. Sometimes the discomfort stays mild and irritating, while in other cases it may gradually worsen with screen use, bright light, lack of sleep, or eye movement. One-sided eye pain that continues for many days deserves attention because some eye conditions do not improve on their own. Reducing screen time and giving the eyes proper rest may decrease strain-related discomfort. Dust, smoke, poor sleep, and rubbing the eye repeatedly can sometimes make irritation continue longer. Avoid using random eye drops or leftover medicines because different eye problems need different treatment approaches. Some conditions improve with simple lubricating care, while others may require prescription treatment after examination. A doctor should evaluate the pain if you also notice redness, blurred vision, headache, swelling, watering, or light sensitivity, especially since the discomfort has already continued for more than two weeks without improvement.