I do understand your problems as sensitive teeth can cause a lot of pain. You do need to brush your teeth 2 x a day preferably using an electric toothbrush and the recommended sensitive toothpaste. If you have tiny pockets round the base of your teeth that is where germs can get in. You need to floss or to use interdental brushes or both. If you can see exposed root, that is the cause of your problem. Your dentist can apply a fluoride gel to protect your roots. If the problem continues and you have a very dry mouth and possibly eyes too, you need to talk to your GP.