i have a friend who did same as you , when she went back on it with the help of a dr it diodnt help her out, she had to change her meds . you might have to do the same. never just go cold turkey on any med.
hope you can get on a med and get back to life.
You suffered a severe withdrawal from stopping too abruptly. Sounds like your psychiatrist understands this. That being rare enough, I would listen to him or her. What is odd is that going back on the Zoloft didn't stop the withdrawal, but these drugs are very individual in how they affect any particular person.
Firstly of course a person should follow their psychiatrist's exact instructions. Varying dosages and titration schedules on your own can make all this worse. If you were stable on the Zoloft for two years it should be fine given enough time. But just keep track of what is going on and keep a mood tracker to see if there are any variances and print out the results for your psychiatrist. For more information on anti-depressents in general google "Depression Central" and speak to your psychiatrist about it.