should i be concerned about this tooth problem?!

a week after the christmas/new year holiday i noticed one of my molar teeth on the top row to the left became suddenly sensitive and still is now. if i drink something hot or cold and it touches it, i get a sudden throb of pain that lasts about a second or two. i have the same problem when brushing my teeth, if the cold water touches it straight away. when i have been walking about in the cold and come into a warm building, i get slight toothache there that lasts for about 10-15 minutes. it seems to be one tooth which i had a plastic filling done when i was 8 years old, however i am nearly 17 and havent been to my dentist since May last year. what is causing this problem, and will it go soon or should i be concerned about it?