There must be local infection of the extraction socket ..visit your doctor he will prescribe you Medicine and local dressing  to relive your pain

After extraction if the wound isn't taken care well it can dry and pain terribly . You should return to your dental surgeon and get it examined , and subsequently he/she may do palliative dressings .

Because the level of infection in The Saliva can never be zero there is always a chance of secondary infection to a healing wound. Please follow the instructions given by a dentist meticulously so that the post operative healing phase is as comfortable as possible. There are some symptoms of localised infection which can be checked by you only---- localised elevation of temperature is the simplest test---- please check whether the cheek on the extraction side is warmer than the cheek on the opposite side and if it is so it is a sign of infection. Swelling and redness in the area will also indicate the same. But even if that is the case the appropriate antibiotics should not be taken as self medication and you should consult your dentist for the same. Regards