Carbo/Taxol/Avastin not working

Hello, I am new to this forum. I have Stage IIIB lung cancer. I have a tumor in my left lung which has spread to a small portion on my right illiac bone. I did 4 rounds of carbo/txol/avastin. I had a Pet scan afterwords which should that this regimen has not done anything. My oncologist now wants to change to Pemetrexed instead to see if that would do anythiung. Does anybody have any thoughts about this.