Depressive disorder is your diagnosis, from what you say. The issues with stress tolerence, concentration, and short-term memory are all symptoms of depression, not seperate disorders. Means you have trouble maintaining you focus, may forget things easily (that were just told to you - this is not a memory problem, but likely you are not able to pay enough attention). Things (symptoms get worse under stress.
Quitting Atarax is no big deal. It is simply an over the counter antihistimine and the side effects make people sleepy, and often feel kind of foggy, and just icky. It has not therapeutic effect.
Zopax is a tranquizer, known as Xanax in US. It helps with anxiety for about 4 hours and then does nothing.
Have you been on other antidepressants? If so, what? Wellbutrin is an odd choice for depression if first medicine tried, especially if you have a lot of anxiety.
Zopivane is a drug for sleep only available in South Africa. Too many cautions for it to be used otherwise.
You are what is to me an unusual combination of medications. To comment on prognosis would be difficult without know a lot more. Generally people can receive relief from proper combination of medicines and do well, but I don't know you circumstances well enough to personalize that to you. Do keep trying and you may have to try different meds. There are so many as people all respond differently to each.