There are a couple of reasons I can think of for why your pumpkins would slow down and stop growing. The first flowers that appeared on my pumpkin plants did not form fruits. The first flowers are almost always male. The pollen on these first male flowers attracts bees and alerts them to the location of the blooming vines. By the time the first female blossoms open, the bees' route is well established and the male flowers' pollen is transferred to the female flowers by the bees.
Male flowers bloom for one day, then drop off the plants.
The male flowers may predominate under certain conditions, especially early in the season, or under certain kinds of stress. The small fruits, visible at the bases of the female flowers, identify them. There is no swelling on the bases of the male flower stems. The variety is Green-Striped Cushaw. Because it has a unique texture, some cooks prefer it for custards and pies.