It's the age. Most babies go through unsettled phases - some only briefly, some for months. It's just part of their adjustment to life on teh outside and the very rapid physicaly and mental development they're undergoing.
In time her digestive system will adjust better. And she'll learn to switch off herself adn block out unwanted stimulation, but for now she needs more help, that's all.
Just be there for her and make sure you're getting plenty of help and support as well.