I am also on Lamictal to lift the mood, and then the Neurontin to help with the anxiety and irritability which has worked for over a year.
I just went to the pdoc because I was describing symptoms like yours- depressed but irritable and snapping at people (boyfriend broke up with me after doing this for a couple of weeks) and the pdoc is calling it "mixed states" and put me on Trileptal.
Fingers crossed for it working.

Good luck.