fed 3 week old cluster feeding horribly?

2-3 days ago my daughter suddenly began wanting to nurse for longer periods, and it's gotten to the point that she wants to eat constantly! Not just at certain times of the day. She'll go on and on until I'm completely dry, and doesn't give me any time to recover. I know I'm not supposed to, but I finally broke down after nursing near constantly for a full 12 hours and gave her a bottle. What am I supposed to do? I have an 11 month old to care for, and I can't just be sitting on the couch for half a day being a pacifier to her.