My molar hurts when I chew something. Help?

Ok so there's this one molar on my left sidethat hurts when I chew something chewy or stickyish like gum doesn't bother it just like snickers or something like that. Is it a cavity?! I checked it in a mirror and it looks normal. No darkieh small hole or anything. I'm going to a dentist in a week but I need to know from you guys first nd if it is a cavity can it be fixed since it only hurts when I chew that certain thing. Can I fix it by just brushing my teeth better and more? Thanks