Have you tried brushing with Sensodyne? It will take a couple of weeks of twice a day brushing until you know if it's working. If your dentist can find any possible cause for the sensitivity after taking x-rays to check for cavities AND to check the root tips for infection there should be no need for a root canal.
By any chance do you grind your teeth at night? Have you been under major stress lately? If you are a grinder (and you may not even realize you are doing it), this too could cause the teeth to be sensitive to cold and chewing. You could see a massage therapist to help you with that or have a night guard made so you aren't abusing your teeth while you sleep.