Teeth hurt when i eat sweets- but no other time. is it still a cavity?

Very likely: Sensitivity to sweets is a sign of a cavity. Get checked by a dentist and treated asap. The longer you wait the bigger and deeper any cavity will get. Small cavities are much easier to treat. Good luck.

Probably: But to be sure, you need to be checked by your local dentist. Please call to make an appointment. Cavities get larger over time if left untreated.

Probably but...: It could also be a defective or cracked filling or cervical or occlusal erosion. Least likely but still possible a crack in the tooth itself.