Why is my dog scared of everything?

Tyrus Asked: Why is my dog scared of everything?

I have a female golden retriever about 14 months old now. When I got her, she was 3.5 months old, she wasn't taken very well care of, they were walking her although she hadn't had her vaccinations yet.

Thing is, she is extremely fearful and timid. She's afraid of everyone, especially men. In fact, I'm the only man she isn't afraid of at all. She avoids getting close to people and backs away if someone wants to get close to her.

Whenever she sees someone carrying something large, she freaks out and gets the hell away from that person. She is also very afraid of some sounds, she freaks out when I step on a plastic bag, she is also extremely afraid of engine/mechanical noise. She sees nightmares multiple times every night, she barks faintly and makes fearful sounds in her sleep so I wake her up. =(

Yesterday, she was spooked from something and she started shivering and she chewed off her leash rope in just 3 minutes, which is pretty incredible because it's a strong leash and it shows just how frightened she was. (I was just a few meters away when she did that, so she could see me and there was nothing threatening nearby)

She isn't afraid of other dogs AT ALL. She plays with even the largest dogs and she sometimes does growl at dogs and show her teeth when she's mad. Very rarely barks though.

Could it be something she experienced before we took her? Maybe someone hurt her? (
If so, how can I fix it and make her feel happy and comfortable at all times?