My DD is 11 weeks and I'm starting to love breastfeeding! The same thing used to happen to me, especially in the evenings as she would cluster feed. She always seemed hungry and my breasts seemed empty, I just wanted to cry with frustration. I just let her feed, it was painful when it felt she was sucking but nothing coming out, but they are just making sure when they go through a growth spurt you have enough milk. It's supply and demand so your body will soon adjust to her feeding whether it be more and less. Try and get rest and drink plenty of water!! I also read somewhere porridge is good for milk production.
It does get easier, I've had bleeding nipples, mystytis, blocked ducts and I can still say I love nursing my LO