My 10 year.old son has cough for a st 2 weeks but starts coughing on my after 6pm. no fever or symptoms. claritan, allegra (fexofenadine) doesn't works?

Long term cough: It does sound like an allergy. Perhaps the combination of claritin, (loratadine) zyrtec or allegra with an inhaled steroid like Flonase (fluticasone) might work better for him. See your pediatrician for further advice.

Post-viral?: Did he have a cold prior to the onset of the cough? If so, there is not that unusual. You may try honey to see if it reduces the cough. If not, consult your doctor since he is likely miserable even though a post-viral cough tends to fade away with time.

Pediatric allergist: This certainly sounds like pediatric allergies and your son needs allergy testing. Ask you pediatrician and ask bout pediatric Singulaie therapy. You can try children;s Benadryl (diphenhydramine) syrup or Zyrtec.

Cough variant asthma: could be that there is some underlying irritable airway disease and shows off as cough because of obstruction to airways. Show him to a pediatrician or pediatric pulmonologist.

Consult Pediatrics: If NO fever, production of Sputum, Wheezing and no Whooping cough, you can try Steam Inhalation with Eucalyptus oil in it,Continue with Anti Histamnic and Add Ginger tea for 1 or 2 more days. Sounds like Asthma. He may need Bronchodilator.