I feel like there is something else I need to do that is missing not just have people give him treats.
Actually, since he's uncomfortable with eye contact and being petted by strangers, it would be better for people NOT to give him treats. If you want to have him around people for socialization it's important that those situations be positive for him, so keep your distance, and YOU give him treats. Instruct people to simply ignore him. Let him initiate contact if he wants to, never force him, and if people insist on staring at him anyway, turn him so he's facing away from them. If he's not happy and having fun, get him out of there and avoid those situations in the future! Over time you may be able to decrease the distance and keep him relaxed and focused, but don't rush the process.
Same with the dog park, he's already had bad experiences there, so please don't continue taking him. It would be better for him to be around dogs that you know (owned by friends, family, neighbors?) are healthy, UTD on vaccines, well socialized to other dogs, and especially, good with puppies. No socialization is better than bad socialization, and exposure to new people/places/things does not require interaction with them.
I would also find another trainer. We have a sub-forum for finding a good trainer, you might want to post a thread there for some suggestions. Talk to your vet about taking him off Prozac. I don't know much about it, but I think you need to do it gradually rather than stopping cold turkey.