Financial talk

Hello. I've had a weird black spot on my tooth for little more than a year or so. I was told it was a cavity, so I didn't think much of it. It didn't hurt, and it didn't grow. I went to the dentist last September for a checkup, and if I had tooth decay I figure he would have told me--however, the little black spot on my tooth wasn't addressed at all, and it wasn't a cavity. Recently, if I chew my food at a certain angle I can feel a sharp pain in that tooth. Now there are two black spots, and the first black spot has expanded a little and turned into a greyish ring. I think it might be tooth decay, but I want your guys' opinions. I cannot, I repeat CANNOT go to the dentist. My family simply doesn't have the money to dish out. Here's a picture of my tooth. I couldn't get close enough to show the spot perfectly, but you can see the big black dot. http://i141.photobucket.com/albums/r78/ruby_the_fire_mage/004.jpg