Re: now I'm nervous I killed my supply
Yeah, I think you're fine, too. Your breasts don't have to be super-full and engorged to be producing plenty of milk. Maybe you are now down to a normal supply, instead of at an oversupply level.
Fussiness can be caused by so many things--it's probably just a phase that will pass. If his diaper output is good, I would not worry at all. You might schedule another pre- and post feed weight or a weight check in a week or two to ease your mind, but I wouldn't worry.
Catherine, tandem nursing mama to Preschooler Girl 9/08 and Toddler Boy 3/11
Breastfeeding for 4 years and counting!