Baby won't sleep!

My daughter will be 5 weeks old tomorrow and she started to sleep very well at night she will eat around 10:30 and sleep till about 3:30 then wake again at about 7-7:30. During the day she is awake for HOURS! Today she woke at 10:00am to eat and it is now 3:00pm and she is STILL awake. I wouldn't mind it much but she is so fussy and cries a lot. I don't know why she won't sleep! I feel like I spend my whole day trying to get a baby to take a nap. Any ideas why she won't sleep or how to get her to sleep would be greatly appreciated!