In the middle of July 2012, my temperature.

In the middle of July 2012, my temperature gauge started going up. I looked under hood and saw the coolant was very low. I filled it up. A day later, it was empty. I added more with some Barrs sealant. It worked. The guage stayed steady till about the beginning of October. The coolant didn't seem to drain fast but it did drain. I put more Barrs and it worked again. However, a few days later, the guage started spiking. It goes almost to the red but then goes back to the middle and sticks. What is wrong? How dangerous is this to my engine. It's been spiking for six weeks and the coolant has not gone done. Need help?