Power pump once a day, it should help :)
Try plenty of skin to skin, pumping doesn't quite have the same affect as when baby is latched but having baby on you can help with that. Also check the flange size on your pump fits you right. I tried giving pumped milk instead of formula and found this same issue in the first few days, I researched everything. Try eating oats, stay hydrated, skin to skin and pump wheb baby feeds to mimic the same schedule. I got more milk using a wearable electric pump than I did the hand held type. Xx
It could be due to the fact baby is no longer latching? Hormones, diet I would speak with your health visitor xx