I was on 100 mgs of zoloft (4 weeks on 150) and we realized it was not working anymore. The Dr. put me on Effexor XR - cross tapering over 10 days from zoloft to effexor xr. Today I took 112 mgs of Effexor and no Zoloft. On Monday I felt fine - zoloft 50 and effexor 75; then Wednesday I felt horrible. Yesterday I felt great and today was the worse day of all. How long should it take to feel better. I am really upset.