Hi. My sympathies are truly with you. Separation anxiety is one of the most difficult behavioral problems anyone has to deal with in canines. I have had a very bad sep anxious rescue dog and I can tell you it takes months of proactive work, which is really hard on owners, to get anywhere close to solving the problem. Medication won't work. I can tell you that straight away. Other devices and equipment will help, but not without a proper program diligently carried out by everyone in the household.
If you are up for it, I'm happy to give some guidance. But I need to warn you, it's a tough journey. The reward is a dog that's happy and contented to be home alone, but equally there are no guarantees, because some dogs just don't respond to it if they have other things going on genetically or behaviorally. And, it may also cause a great deal of stress on you and your family, because there will be sacrifices in time and effort - and that's assuming you are able to undertake the program at all, given that it needs an initial period of time when someone needs to be at home.
Oh my goodness! Sorry to hear this. I was reading about the doggie vests that are supposed to relax them. Now, if you aren't aware of the theory regarding deep pressure, this probably sounds insane. But I have a son that has some special needs. A pressure vest or tight fitting weighted vest is a calming tool. I thought it fascinating that they are now bringing that to the animal world. Research it. That tight squeeze is supposed to slow down the nervous system a bit. It works for my son. :>). Something to use along with the antidepressants. And I'm sure you've thought of the obvious of having a tv on while you are gone for company. Do you confine him to a particular room. I would doggie proof a room and have that be where he stays. Try to get a break from work to come home mid day to check on him and reassure him. good luck
My only suggestion is to continue the doggy Prozac, once he gets to a calm point you may be able to ween him off of it. In the mean time, work with him by leaving for short periods of time. Separation anxiety is a difficult thing to over come but it is possible.