My heater blows cold and keeps over heating.

both symptoms indicate a low coolant level. Losing your heat is an early sign of low coolant. the heater is higher than the radiator so it will get air in it first and stop being hot. Also low coolant can either be a cause of over heating or a result as in the unfortunate case of a bad head gasket.

I have no water in the oil and have lots of antifreeze don't understand why it keeps overheating

Another less likely problem can be a faulty water pump. Low flow or no flow will cause both an other heat problem and since no coolant is being pumped through the heater core you will have no heat. An obstruction in the radiator would cause an over heat but not poor heat from the heater and coolant would still flow through the heater. you need to establish weather the coolant is flowing sufficiently.

thank you for all of your help is there a way I can determine whether or not my water pump is working correctly

Flush out the cooling system. I had nearly the same problem. Replaced the water pump, thermostat, etc. didn’t fix it until I flushed the cooling system.