Yeah, you absolutely have a clog somewhere in your cooling system. The only time I didn' t have heat, my car had overheated because there wasn't enough coolant in the system to pressurize it (and therefore raise boiling temperature), so it all just burned off and I had _NO_ coolant in my engine. Yeah, I blew a head gasket. So make sure that you at least have coolant (sounds like you do), and if you do, then you've got blockage.