Effexor is a great medication but you were on a high dose and I believe you came of it way to quick,you need to taper slowly.
I personally think that the symptoms you are experiencing is withdrawal from the Effexor. You were on a large dose, and it will take quite a time to get it out of your system. If you have read other posts about withdrawal from Effexor, you will see that it is difficult. You could go back and see the doctor about this, or sit it out, and wait to feel better. Some people say it takes quite a time, but in my case, I was on 150mg daily, and did withdraw at once. I had never heard about all the withdrawal symptoms, and in my case I was feeling better after a couple of weeks.
My depression came back after a year, and I am on Effexor again.
I think maybe you should see the doctor again and say you are having bad withdrawal symptoms from the Effexor. Also as you know, anti-depressants take a time to take effect, so with the Welbutrin you are effectively starting again, and it will take at least 4 weeks to feel their benefit.
Talk go your doctor about the side affects it may be from the dr taking you off of it that fast. Make sure to make an appt. as soon as possible and tell the doc what is going on..