Everyone is different. You may either be on the wrong anti-depressant, or need one of the combination antibiotics. Are you seeing a therapist? The medications nowadays are good, but they can't completely take the place of figuring why you are so unhappy and finding a strategy to deal with the cause.

Also, tolerance can build to certain drugs, though its unlikely with that time frame. I agree with MdngRain. Definately talk to your Dr. ASAP. Usually if you are changing from one anti-depressant to another, they will give your body a little time to completely get rid of the first anti-depressant. If you are feeling suicidal, the sooner you get in touch with your Dr., the better.

Sam2