A persistent dry cough after a viral fever is very common and is often due to temporary airway hypersensitivity or post-nasal drip. Since over-the-counter syrups haven't worked, you may benefit from targeted prescription treatment. Doctors often prescribe steroid inhalers (like budesonide) to reduce airway inflammation, or antihistamines combined with nasal sprays if post-nasal drip is the cause. Please consult a physician. They can examine your chest and may suggest a short course of an inhaled bronchodilator or a stronger cough suppressant like dextromethorphan. Rest assured, this 'post-viral cough' is highly manageable and usually resolves once the airway inflammation subsides.