She won't stop crying!! HELP!!

I don't know what to do!! My daughter has been cranky all day & hasn't slept much at all like she normally does. She usually sleeps for about 2-3 hours and wakes up for a diaper change and feeding and falls back asleep. Today she hasn't slept for more than half an hour at a time & wakes up screaming. She's 12 days old. I feel so helpless & lost & want to comfort her and help her feel better. Anybody have any ideas what could be bothering her?? Any advice will help. I hate seeing her cry.