16 mths baby frequent fever

My 16months baby been having monthly fever episode since 8 months old and each time, lasts for at least 5 days with high fever (highest at 40.2 / lowest at 37.7). Thing is, everytime before his fever - he would drool badly (like his entire front shirt would be soaked wet!) and chewing his hands for 2 to 3 days. Though doc always say its viral and teething does not caused high fever. Anyone has such experience to share? I'm worried with the frequent fever.. but his blood test result came out okay..