The filling of tooth doesn't last more than 6 months depends on the severity of tooth structure lost and the position of the tooth in the oral cavity . If simple filling doesn't stay then u might need to go for an only or inlay or may require a cap to restore the lost tooth structure .
Next Steps
kindly visit a good dentist
Health Tips
try avoiding biting hard food on that particular teeth .and get a cap done on that tooth if filling doesn't stay