50 of Trazodone doesn't work? Talk with vet, up the dose. That takes care of the nails, but the reason concerns me.
The larger issue here is why this would suddenly create such an intense issue, or at the least, exacerbate it. Yes, they do not generally like getting clipped, but once accustomed to it, you typically get the same reaction. I think in this case, you might want to look further into the change. Maybe he hurt one of his fingers and the next time you went to cut them, it caused excruciating pain? Like our toes, it doesn't take much to break one, and the pressure from the clippers can create bad pain. And, once he associates the clipping to that pain, it's all over.
I'd do two things here: The first is have the vet take a look. And the second is to take a step back, and de sensitize him to your touching his paws by first just gently brushing them with your hand, offer reward/praise/bribe, and then slowly up the contact as he tolerates it, eventually reintroducing the clippers w/o actually clipping. This will take a while, have patience.