I went to the dentist for a toothache and he said it wasn't a cavity, nor nerve issues. if it is neither cavity nor nerve, what could cause my tooth to hurt so badly?

Sensitivity: It could be sensitivity. Tooth sensitivity occurs when dentin, the underlying layer of your teeth, is exposed. Dentin is porous and allows hot, cold, sweet, and acidic substances to enter and stimulate the nerves and cells inside your tooth, resulting in discomfort. Sometimes this occurs right at the gumline. Use sensodyne or a desensitizing toothpaste and rinse with Fluoride mouthwash.

Gums? Crack in tooth: Many of my dental emergencies involve issues with the gingiva (gums) and bone or with fractured teeth. If your tooth hurts upon biting, a crack is a possibility. If the gums are bleeding and swollen, gum disease is suspected.

Maybe cracked: Your tooth may be cracked. It's hard to see that on an x-ray, and even sometimes with visual inspection. If the pain doesn't stop, ask your dentist to check for a cracked tooth with a light. When shined on a cracked tooth, we can see where the light shining through gets blocked.

Multiple: Could be fractured tooth, exposure of the root to the oral environment, hyperfunction from grinding or malocclusion, or a high filling in an opposing tooth. Might want to have an endodontist check it out.