My tooth hurts when i suck in air. what does this mean?

Nerve exposed: Your problem is likely the result of either a cavity or gum recession with exposed root surface either of which can be detected and treated by a visit to the dentist. While a decayed tooth is more serious, sensitivity from gum recession can be indicative of a serious gum problem so that also requires a prompt evaluation.

Root sensitivity: As long as the pain subsides when you take the cold air away it is likely a minor reversible issue. Exposed root surface or a missing filling opens the inside layer of the tooth called the dentin. The dentin has no nerves in it but it has microscopic channels that reach the nerve. Those channels react to things like cold air, ice and sweets. Desensitizing toothpaste and get fillings checked.