I am at a loss for what to do with my dog. He is a hound mix about 4 years old that I rescued. When he first came home, he was immediately attached to me and would never let me out of his sight. He was terrified of my then boyfriend and it took awhile for him to warm up to him. There were only one or two other dogs that he saw at my apartment complex and they never really met or played. He met my parents dog, a yellow lab, and fell in love with her. He is very shy around people. He likes women, but will shy away from any men, even if they aren't looking at him or are near him. When my now fiancé came into the picture, he warmed up to him quite fast which surprised me.

Since he is so shy, I started trying to socialize him only after a few weeks after bringing him home. I took him to the dog park, took him on frequent walks where there were people, and I take him to PetSmart to walk around and meet other dogs. Nothing has worked. He gets so freaked out and starts shaking when other people are around and if other dogs come around he immediately clams up and starts shaking, and if the dogs come near him, he goes into defense mode. He starts growling, showing his teeth, puts his ears back and starts snapping. He has never bitten any dog, cat, or human before. They never have to muzzle him at the vet or groomers. He only gets defensive when other dogs come around, he has never growled or snapped at any human.

He is terrified of most noises and if we go outside at night to go to the bathroom and he hears a noise off in the distance, he shuts down and won't pee or poop and pulls on his leash to go back inside. He is terrified of thunderstorms, which I understand, but if he hears any loud noises in out apartment, he shuts down, runs away and hides and starts shaking.

I've tried everything I can think of to help my dog become more social, but nothing has worked. He is trained and knows all the basic commands, is house broken, and knows that I'm the "pack leader." Dog owners of Reddit, I need your help. I don't know what to do. I don't want him to be a shy dog that is the equivalent of a cat. I know that he was more than likely abused before I got him by his owners and most likely other dogs, but since he's been with me, he has never been harmed. It's frustrating because I just want him to be a happy playful dog like every other dog, but he's so afraid of everything. Has anyone had the same issue and used the doggie version of Prozac? Has it helped? I just need some advice!

EDIT: I've taken my dog to the dog park and PetSmart on several occasions over the 4 years I've had him and one day he will do great, and the next day, he will flip out and nothing has changed. Same amount of dogs at the dog park and same amount of people at PetSmart. It seems like he just has an on/off switch in his brain, one day he is great and walking around sniffing and then the next day he is shaking and freaking out. This is happening constantly and I can never predict what he is going to be like that day.