Why are pin 18 and 19 always HIGH? I wired my switch just like in the default button program. I know it works because it works fine on other pins, just not pin 18 or 19. What am I doing wrong?

const int buttonPin = 18;     // the number of the pushbutton pin
const int ledPin =  13;      // the number of the LED pin

// variables will change:
int buttonState = 0;         // variable for reading the pushbutton status

void setup() {
  // initialize the LED pin as an output:
  pinMode(ledPin, OUTPUT);      
  // initialize the pushbutton pin as an input:
  pinMode(buttonPin, INPUT);     
}

void loop(){
  // read the state of the pushbutton value:
  buttonState = digitalRead(buttonPin);

  // check if the pushbutton is pressed.
  // if it is, the buttonState is HIGH:
  if (buttonState == HIGH) {     
    // turn LED on:    
    digitalWrite(ledPin, HIGH);  
  } 
  else {
    // turn LED off:
    digitalWrite(ledPin, LOW); 
  }
}
The analog pins function as digital pins number 14 - 19, with 14 being A0 and 19 being A5. I had hooked it up backwards. 

This time we're gonna get funky
Everybody check your pins
Check check check check your pins
Check check check check your pins