I don't know if it's just coincidence, but I started pumping today too because of the pain of thrush when Danny ate, and because of the stupid day not being convenient, we had to do a lot of mixing in formula in his feedings too. around half-half I'd say. He was ornery and refused to go down easily (never had this issue before), and I was thinking before I saw this thread that it was tummy cramps from the different foods. I've read that breastmilk digests quickly, and formula is a bit slower, and so thought maybe his stomach and intestines had gotten confused.
Have fed the last three feedings of breastmilk only (thank god for the return of convenience) and he's now FINALLY sleeping like a rock.
So I dunno. Could be either I guess, and it could be just your baby's way of reacting to the day, whatever kind of day you had

Hope things are going better!