switching from zoloft to wellbutrin

I have been taking zoloft (50mg) for many years, i am tired of the weight gain, sexual side effects and other.  I talked to my Dr 12 days ago and he suggested that I immediately switch to Wellbutrin XL.  I asked about tapering and was told that it was not necessary.  The first 5 days was fine.  For the last few days I have been extremely irritable, had headaches, dizziness, and many other symptoms i am now finding may be related to Zoloft withdrawl (withdrawal).  Now that it has been 12 days, is it too late to try to taper the zoloft, should i go to 25 for a time first? If I am coming to the end of this icky feeling I would wait it out but I don't know how long to expect to feel this way.
Any advice?

[Roger Gould, M.D.]

It may last for weeks, and there is no in going back to 25 mg every other day for a week, then stop again..that should do it.