Has the fatigue just been since you've been taking the Latuda? I don't know anything about that drug, but I know lots of psych drugs can cause sleepiness and/or contribute to depression. Or maybe it's the combo of that plus the Zoloft.
Did your doctor check your iron and B12 levels? (Iron should be in a regular blood panel--well, at least anemia would show up in the red blood cells part--but not B12).
There's a lot of drugs out there, and different people react differently, so unless you've tried most of them, your pdoc should at least be able to come up with something to try. Have you tried other SSRIs? Or SNRIs like Cymbalta?