Tooth cavities, not sure if I have it?

I think or don't think that I have cavity on my tooth... I don't know. Before I decided I had cavities, I went to the bathroom to check where I felt pain. What I saw wasn't a hole on my tooth, rather, all the way into my mouth, I saw a hole on my flesh but really close to the tooth, and it only hurt (not much), if I bite with strong force. When I do that, I can feel saliva mixed with what I ate come back. So my conclusion is that, I have a hole on the flesh at the right side of my tooth, where my saliva and mixed with what I ate, is in there. So... is this cavities or something else? How can I fill that hole (not on my tooth, rather on the flesh)? Thanks...

Update: Forgot to mention, the hole isn't big at all, but its visible and my saliva can enter it, including air...
Update 2: It feels like the pain is slowly fading away... but I still feel insecure of cavities. Please, anyone talented/experienced or who knows about this, please let me know.

(2 days later, no response from above): The hole is not above the wisdom teeth, not beneath it, not at the left, but at the right. The hole is at the right of the wisdom tooth, not on the tooth, more on the flesh. The hole is not big either, it's like a sharp pencil at the end where you write. But if I clench my teeth hard, I can feel my old saliva (if it is) and the food I just ate come back from the hole... It feels like its being stored in the hole. Is this cavities or something else?