C.G.
Has he been in daycare long? Some babies will reverse cycle- they prefer to get their breastmilk "from the tap" (or in this case from Dad too maybe) and will just eat more when at home and less when at day care. Maybe that's what he is doing? Do you think he is eating more than he used to in solid food at day care? It may be that he is eating a lot of cheerios or other finger foods and they don't realize how much he is having. As long as he seems to be well hydrated and healthy I wouldn't worry and maybe freeze some of that fabulous extra EBM for later. Also the site www.kellymom.com discusses reverse cyclng. Good luck.
BTW my best friend is a "mum" from England and just moved to Germany- you're making me homesick for her:)