For a while now my heater has stopped working when I come to a stop or if the rpm is low. in the past weeks I have noticed that when i turn on the heater or the engine begins to heat up after driving it for a while the temp gauge will rise and then start to overheat but then it will quickly drop down (like something kicked in). Now, yesterday my car started to overheat and the gauge will not come back down when driving. Water Pump? I changed the T-stat within the last four months so I don't think thats the problem?

Well it would help to know what year model and engine you have.

 

But given what you said, I'd say you are:

 

- Low on Coolant (leak bad Head Gaskets...)

- Check the coolant when the engine is cold, is the over flow bottle up to the required level? Pull the cap, is the Radiator Full?

- Check the overflow bottle for black oily stuff, a sure sign of a HG leak.

- Get you coolant system pressurized

- Get you coolant system checked for signs of Exhaust gases, NAPA sells the kit for $70 or so.

- If all that checks, it could be the thermostat, water pump or plugged radiator.

Has the coolant system been maintained?

It does sound suspiciously like low coolant...