You may need to try different meds before you find what works. Keep in contact with your doctor so that s/he can make changes. I have not had this reaction myself, but everyone is so different.
It is normal to feel better during pregnancy. During pregnancy your progesterone goes way up and that hormone helps so much with depression & anxiety. I think that is when I felt the best. Coming off that high progesterone is, I think, why so many have the post partum depression.
Hope that you are feeling better soon!