Your teeth may be just be sensitive to the ACV or it may be that the ACV is affecting your enamel. If you are worried, I would put the ACV in a small glass of water, drink it in one go, then brush my teeth and rinse.
You may also want to consider brushing your teeth with something besides toothpaste. Almost all toothpaste contains glycerin that coats your teeth. You can't see or feel it, but the theory is that the glycerin prevents your saliva from re-mineralizing your teeth.
There are many recipes for toohpowder on Curezone and the Internet. You may also want to consider using soap--no kidding. A vegetable based soap can be used to brush your teeth. I bought a bar of olive oil based soap and use it occasionally to brush my teeth. It make a difference immediately. A lot of people were posting about this on Curezone a few weeks ago.