Thanks for all these suggestions! I think I've been washing too many pads at once, should maybe use vinegar in the rinse cycle, and wash twice if they've been sitting for any amount of time.
For those who PMd me, I use either the white hospital pads or the laminated pads from EZ Whelp. I LOVE the laminated pads, they are brown on top - which looks kind of nicer; they are SUPER thin but absorb a crazy amount of liquid; I also love that they lay so flat and keep their shape, whereas the hospital pads sometimes look wavy/wrinkly. These are the laminated pads:
Buy Waterproof Pads for Whelping
What the heck is Dettol? Never heard of it.