Sorc here, but what you said just doesn't make any sense. You say that you are being attacked by two or three AND you should be able to fight back? If there was any class that could handle 2-3 people attacking them, and be able to fight back, it would have to be a tank, but they still have kill all of them.
I am a full Champion Sorcerer and I have a hard time dealing with Mercs, Marauders and Operatives. But that is cause they are the rock to my scissors. I cant take tracer missile because I am light armor, the damage that a Marauder can output is just too much for me, and Ops stun lock me day all the time. I don't QQ though, because there should be counter classes, other wise this game would be all about zerging.... wait.... whatever. There is a reason Sorcs kill you, cause they are your counter class.