Q.grapes small
grape plants are large but berries small but plentiful

Certified GKH Gardening Expert
There are many, many issues that can cause these symptoms. I will include some links to some articles that will get you started in figuring out what is going on with your grapes: https://www.gardeningknowhow.com/edible/fruits/grapes/how-to-get-grapes-on-vines.htm
https://www.gardeningknowhow.com/edible/fruits/grapes/treating-grapevine-problems.htm
https://www.gardeningknowhow.com/edible/fruits/grapes/preventing-pierces-disease.htm
https://www.gardeningknowhow.com/edible/fruits/grapes/treating-grapevine-problems.htm