Doesn't heat

[crimson red]

I have a 03 grand prix gt with only 88,xxx miles on it. I've been having problems with it not blowing out hot air. I can switch it and it blows cool, but once I switch it to hot, it stops. Hot air slowly comes out when the thermostat is in the off position. I could use some help in figuring out what is wrong with it, before it takes a turn for the worst. Thanks

[Explicit_Spade]

Do you have a heater core?

[crimson red]

It worked when I first got the car. I got it over the summer so I didnt use it.