It doesn't sound like the Zoloft is helping much if you ask me. I'd suggest going to another medication if I were you. Even if the dosage was increased, it sounds like the likelihood that your numbness would increase, too. I had the same problems when I was on Zoloft. When I was younger and took Zoloft I was always upbeat and couldn't seem to feel anything but "happiness". After years of being off it I went on it again since it seemed to help before and did nothing for me. Much like you have described.

I'm now on Cymbalta, which seems to be helping my depression. It's a newer type of medication, called SSNRI's. (Selective Seretonin Norepinephrine Reuptake Inhibitor)

Good luck.