SRT - Cavies are prey animals so they always tend to be scared of anything loud and large. I've had some of my cavies for almost two years and they still run and hide when someone walks in the room. As soon as they are being held they settle down and are snuggly.

Deandra is right that your pig is still adjusting to it's new environment. Try feeding him some veggies by hand so he'll associated your hand with food. It may help tame him up a bit quicker.

Also as Roozy pointed out you may want to look into adopting a same sex guinea pig to pair up with your current pig. Cavies are herd animals and very social. I think you'll see a positive turn around if you adopted another.