My teeth are so sensitive it hurts to eat. i have no fillings or known cavities. what do i do?

Last checkup?: See a dentist who can give you a one on one examination, take some x-rays and determine the cause of your tooth sensitivity. We can't do that over the internet as much as we would like to. There are other causes of tooth sensitivity other than cavities or existing fillings.

Clenching/grinding: Is it possible that you are grinding or clenching your teeth? This will often cause sensitivity. I would also not use any tarter control or whitening toothpastes as they can make the sensitivity more pronounced.

Dental Exam: What you are describing is not normal, but without a dental profession doing a comprehensive exam, imaging studies (x-rays and photos) and study models, there is no real way to give you an answer and a solution. So follow-up and seek out a dentist's help! i'm sure there is a cure for you!