How to help my kitten go to sleep?

I found a tiny abandoned kitten a few days ago, I guess she's about a week old. For the first two days she spent most of the time sleeping, but yesterday she kept me awake all night, crawling around in her box and crying. I don't know what the problem is - she is fed and watered, warm and dry (doesn't have a fever) and she goes to the toilet regularly. She also began scratching my hand quite hard when she's feeding, she seems restless all the time and it's quite heartbreaking. Do you know what could be wrong and how to help her (and me) have some sleep? Thanks for suggestions...