If you have been watering and fertilizing around this cherry tree and it isn't producing large cherries it could be one of a few issues. When one cherry tree or variety does not have another to act as a pollinizer the fruit will often not develop. Usually the fruit never sets without pollination. A second possibility is a virus disease that can infect a tree. It can lead to what you describe, all pit and almost no fruit. You can not reverse this if it is a virus. Hopefully your tree has one of the treatable problems.