Please help! tooth pain but the dentist says nothing is wrong?

Wait or do something: It is hard to help without specifics. Get a second opinion if you don't believe what your dentist is telling you. However, if the dentist advised you to wait and then follow up with him or her, you should definitely do that. Sometime, it is hard to diagnose something right the way and you body can heal itself as well. The key is to follow up. You shouldn't be in extreme pain though.

If there's no cavity: No evidence of pathology in the x-ray, pulp test is (-), it can be a toothache syndrome related to a temporomandibular joint dysfunction caused by referred pain.

Cracked tooth ?: Very often one can have tooth pain from a microscopic crack in a tooth, that will not show up on an x-ray. Diagnostic test like percussion, endo ice, transilumination, electric pulp testing can all help to isolate the correct tooth. But if you have this problem, you and your dentist can work as a team to discover the correct tooth and than your dentist can devise the appropriate treatment plan.

See an OFP: Toothache of nonodontogenic origin is not true dental pathology; rather, it is pain referred into the dentition from a distant location (e.g. sinus, TMJ, muscle, nerves). See an Orofacial Pain practitioner for diagnosis and treatment.

Something is amiss: But more info would be helpful. Pain to cold or sweets? Pain on biting down or tapping tooth? Did tooth have root canal therapy? Maxilary or mandibular tooth? Sinus issues? Answers to these questions are vital to providing you a meaningful response. Without this info, your best bet is to have the tooth evaluated by an endodontic specialist.