Growth spurt at 3 and a half weeks?

My daughter will be 4 weeks tomorrow and has been pretty consistent in her feeding pattern (every 3-4 hours) until the last couple of days where she has been wanting to feed sometimes as frequently as every hour. I was wondering if anyone else has experienced this at about this age and if this a sign that she is having a growth spurt or could it be a sign of something else? (We are doing a mixture of breast- and bottle-feeding if that has any effect).