How Can Severe Anxiety Be Treated?

I have ptsd manifesting itself in anxiety that is not constant but just comes out of nowhere and is terrible. It can happen any time of day or night. I was taking Sertraline but it caused cronic diahria, sweating and shaking which I understand is a rare but real side affect. After 7 weeks of diahria, I backed off the med and am now just taking a welbutrin extended release and a prozack 20 miligrams which has had no impact on the anxiety. My therapist mentioned Lexapro and said that it is one of the only meds that is specific for general anxiety rather than depression. Is this accurate?