I agree with Deb. At around the age Grayson is now, Lilah started to really cut down on the amount of time she nursed. I had a lot of milk and a very powerful letdown. She would bob off the breast and maybe humor me a couple times by latching back on, but not for long. If I pushed too much, she'd arch her back and scream! Now it seems pretty clear to me that she'd eaten enough, but back then I would flip out, thinking she hadn't, just because she was nursing for so much shorter a period than a baby her age was "supposed" too.
HTH!