Hello sir,    Dry mouth may be due to many cause      due to intake of certain medication,smoking,tobacco chewing,rarely nerve damage due to injury,fever,not taking plenty of water,excessive sweating,sleeping with open mouth, dry hot wheather,eating dry hot foods....    Throat infection mostly due to bacterial  infection...     

For throat problems consult a good ENT doctor. For dry mouth consult a dentist to rule out any oral issues.