Certified GKH Gardening Expert
You may be picking the fruit too early. Do not pick them as soon as they turn blue. Wait a few more days for them to fully ripen and grow larger and sweeter.
Also, follow the fertilizing schedule in the article below and the importance of acidic soil:
This article will help with the care of blueberries: https://www.gardeningknowhow.com/edible/fruits/blueberries/growing-blueberry.htm