Toothache since January?

My boyfriend has had toothache since January so for 6 months now. He brushes his teeth twice a day and has been to the dentist to get it sorted a number of times. They took two teeth out and he had some fillings but still he has the pain and now pain killers have stop working so his pain won't go away. We don't know what to try to ease the pain or what might be wrong it should have gone by now but it just won't. We are very thankful for any help or advise you can give thank you.