Is this physician a psychiatrist (MD) or a general practitioner?
You mean 50mg of Zoloft, not .5mg (no such dosage)! 50mg of Zoloft won't do much for you.
If you are having "acute anxiety disorder", Zoloft (SSRI) is not really the optimal medication for treating anxiety (by itself). I am surprised you are not being prescribed Effexor XR or possibly a Tricyclic like Pamelor. My guess, Effexor XR and Zoloft would probably work best for you. For example, 75 - 100 mg/daily of Effexor XR with 50 -100 mg/daily of Zoloft would be a good place to start for the next 30 days (your doctor is the ultimate decider). You should not need the Xanax.
Every antidepressant uses a different mechanism/path on the brain.
Xanax - is typically used for a panic attacks (acts like a sedative), it's not for long term use to treat anxiety. Xanax is similar to Ativan.
I would suggest while you are "fine tuning" your medication(s), try maintaining a daily journal. Hopefully, you are also getting counseling.