Boy, it is hard! My difficult child, 17, has been on many, many medications, in many, many different combinations. I think that there are some I would never put him back on, just because there were dramatic side effects - and others - maybe I would try again because in retrospect, maybe there was not enough time on the medication to make the best decision.
It does sound like your difficult child, in my humble opinion, is not suffering so much from ADD, but from some sort of mood disorder. But, you know, I am just speaking from personal experience - and am obviously not there or a doctor.
For my son, it has been a road of many trials........last May he was in phosph and we tried the current medication combo, and it seems to have been the best overall. His mood is moderately controlled, maybe 2/3rds of the time - and he has no side effects, that I can see, which has not been the case for years. (No lethargy, weight gain, etc.) Not perfect, but better.
I think the mood stab is key, for us it was Lithium. Then we added Lamictal, and the Clonidine............and finally when the mood was somewhat stable, we had to address the depression and anxiety with Paxil. Of course, every body is different, and I cannot recommend one or the other - I just know it took us many, many trials and errors to find something that worked even 2/3rds of the time.
Keep up the good work, and just continue to be open minded about all of of the possibilities.
Hugs.