Hi Nee,
I was just looking up something in my BWSAYP book and came across an example that is similar to your situation. In the book (I'm paraphrasing and it's pages 197-198) it states that if your LO has slept 5-6 hour stretches at night and was sleeping well and suddenly started waking up and downing both breasts, the cause is a growth spurt. It is a food problem not a sleep problem. As a solution, it says to try upping the food intake during the day. Don't enourage the night time feed as you are setting up a pattern of accidental parenting.
I hope this might help with your night waking.
Mel