Adding lamotrigine might do the trick. Personally, I'd try that before adding a second antidepressant.

What does your Pdoc think?

(If you end up trying more than one thing, try one thing at a time. Making more than one change at a time makes it impossible to know what's causing what, whether it be a positive effect or a negative one. Seems common sense, but you'd be surprised how often it's done.)

Good luck!