What is wrong with my car i am completely stumped..?

Well i have a 1993 plymouth Acclaim.. At first my car would overheat so i changed the thermostat and that didn't work so for the summer i just kept the thermostat out. now i have a thermostat in and i have heat again but it only works every now and then.. Sometimes the heat works and sometimes it doesn't same with the overheating sometimes it works and sometimes it doesn't. I have been told thermostat blown head water pump and heater core. Someone pleasehelp