Seriously - if you've tried flossing and cleaning your teeth carefully (to see if you have some food stuck between them), and there's been no change, then I think a visit to the dentist is imperative. If you have a small hole in the tooth, then it won't get better by just leaving it, and could actually result in you getting an a gum infection or an abscess. You can buy temporary "fillings kits" from a dentist, and I believe Boots sell them, but they're really only for emergencies, and only a dentist can examine you properly and tell you what's causing the problem.