1991 Pontiac Tempest coolant leak

My car was over heating and not keeping any coolant in at all. Someone checked and said its not the rad or water pump. They told me its the frost plug but had no idea how to get at it. My oil is not milky looking and it seems to be leaking from underneath the engine somewhere. I dont have alot of money so I cant take it in to get checked. Someone please help me. I need to know how to get at the frost plug or if its something else?Thank you