Sometimes you feel pain or discomfort when you:

Drink a cold or hot beverage
Take a drink from a cooled water fountain
Suck air through your teeth

The leading causes of tooth sensitivity

Incorrect brushing technique (see our article on tooth brushing)
tooth grinding
Drinking too many sodas, or other acidic drinks (remember to wait an hour before brushing after consuming these!)
Overaggressive use of tooth whiteners (which can thin your enamel)
you might have a cavity

If the tooth sensitivity does not go away or get better, you should see a dentist. If it's a cavity, the sooner they deal with it the better. If it's not a cavity, a dentist can bond the sensitive areas (which acts a sealant layer on the exposed dentin, preventing problematic external interactions from causing you pain).