Dull tooth ache with biting and pressure?

I was at work yesterday and randomly my front tooth started to ache a little, but it wasn't bad, very dull...but at lunch I went to bite into a granola bar and it hurt! Ever since then I've had a dull ache in my tooth whenever I put pressure on it with my tongue, and it becomes more of a pain when I bite into food. I'm hoping this is just a temporary problem, but I'm assuming it's not. I can't stop thinking about the terrible things it could be. If you could put my mind at ease, it would be much appreciated. I am going to the dentists next week.