First 2 weeks were easy...What happened?

aimalama

My daughter will be 3 weeks old tomorrow and she is a totally different baby this past week.  At first she was really easy, eating every 3 hours and sleeping in between.  Ever since last Wednesday she has been wanting to eat every 1.5 - 2 hours and in between feeding she just cries - like red in the face screaming and crying.  We have tried so many different things and what mainly works is just laying down and holding her against your chest.  She'll fall asleep there, but when you get up to put her in the swing or bassinet her eyes pop open and shes back to screaming crying.  Is this normal?  Is there something more that we should be doing?  When she is alert and is calm I try to talk with her or do tummy time, but to be honest I'm so exhausted that I just try to get her to go to sleep.  I am breast feeding and at the appointment last week her weight was well above her birth weight and the pediatrician felt that she was getting enough milk.  She has tons of poopy diapers and wet ones.  Is it my milk?  Is it gas?  Any advice would be helpful.