Sensitivity of the teeth can be because of multiple reasons:
1) Too hard brushing or brushing your teeth with a hard brush can wear off the proctective layer of your teeth called the enamel which can lead to sensitivity.
2) Rubbing of acidic food , baking soda etc can wear off the enamel.
3) Drinking Aerated drinks on regular basis.
4) Conditions like hard clenching or bruxism