My guineas are very new too- I've had them for 2 weeks today. They are eating normally now, but are still quite skittish and tend to run and hide when I open up the cage to say hello or feed them. They do come out after a few seconds to eat, and eat right in front of me now. I'd say just to be patient, it takes time for them to begin to trust you and get used to new surroundings. It's the same with any animals really.
My guinea pigs are rescues; a mother and daughter pair. Pikki is the baby, about 5 weeks old. Nola is the mother, we think she's around 7 months. They were both found in a bin, and Nola has obviously never been socialised in the past as she is very reluctant to be picked up. Pikki, however, has been socialised from quite a young age and is now getting used to being held.