What should I do for a cough that has been persisting for nearly 3 weeks (tested negative for COVID)?

Persistent coughs can be concerning, especially if they last for several weeks. It's important to rule out any underlying conditions like lung infections such as bronchitis. If your cough continues for more than two weeks and is accompanied by colored secretions, it would be advisable to see a doctor for further evaluation. They may recommend antibiotics or other treatments based on their assessment. In the meantime, you can consider using an expectorant syrup and saline sinus rinses to help alleviate some of the symptoms. If you have any known allergies or are currently pregnant or breastfeeding, be sure to mention this to your healthcare provider.