I really need some serious help because I'm really freaking out!!?

Okay okay. I'm freaking out really bad. I'm 16 years old. When I was a child I guess I didn't brush ym teeth alot but now I'm getting into the habit of doing it at least twice daily. But my teeth are breaking up! Like, I was just about to eat a pistachio and when I bit down, my tooth in the back broke off a little. I don't know what to to because I'm taking care of them. My family doesn't have money to go to a dentist and we haven't been in years so I need to know how to make my teeth a lot stronger. I really am going crazy with fear and stuff because what if I'm like 30 and I have to have dentures? It's sick and I'm terrified now. Please please help me. If you want to email me, my email address is ocea_blu@yahoo.com.