Why do my teeth get really sensitive when i suck on candy?

Stimulus to nerve: When stimuli, such as cold, hot, sweets, etc penetrate the outside layer of your teeth reaching the dentinal tubules inside your tooth, it allows stimuli to be transferred to the nerve of the tooth. It may be from cavities, leakage around fillings or exposed root surfaces. This stimulus is transmitted from the nerve of your tooth to your brain and perceived as pain. See your dentist for exam.

See your dentist: You have some sort of problem either leaking fillings , cavities or exposed roots to name a few. Get to your dentist and stop sucking on candy you'll be the healthier for giving that up....