There could be a tiny little cavity causing sensitivity. Does your dentist use digital XRays? They can see a lot more than regular XRays. (Which can be good and bad, but good when you have a problem like this.) I had it happen recently.
I agree with the Sensodyne. It has something in it that dentists use to help with the pain. You haven't been whitening lately, right? That can cause major sensitivity. Colgate also puts out a rinse (I forget what it's called) but it helps with minor mouth pain. Make sure you are flossing really well. They also make those little plastic things that look like screws that you can use in-between your teeth to get them really clean, then rinse for a minute or two. My dentist also prescribed PhisoHex rinse.
Good luck.