Pain in tooth can b due to many reasons.Firstly due to cavity. Secondly due to irritation to the gums which may b due to food lodgement. Other reasons may include fracture of your tooth. Please visit dentist so that the tooth can be treated accordingly.  

first comes the nature of the pain i.e. pain occurs while only chewing or any time of the day or night, how long does it remains pain, whether it subsides itself or u require a pain killer, as it can occur due food impaction or due to cavity or last molar tooth eruption. get a check up by a dentist and also get an x-ray done if required by dentist as soon as possible 

may be u have cavity in ur teeth or it may be a fracture of tooth ,or it can be due to gum infection  ,get it checked with dentist immediately ,and try to avoid chewing from that side till u visit a dentist.