Maybe I misread but I got the impression you are having to prune often? If so, try to reduce the amount of pruning by half? The stems will slowly become stronger with the passage of time. When you prune often, the new wood will not have time to support the weight of the blooms and may have the problems one experiences with hydrangeas like Annabelle, whose weak stems cannot hold the blooms straight up when they get wet. Leaving the stems unpruned helps Annabelle stems support more weight as they mature in a few years. In the meantime, if you get too many blooms in clusters, you could strategically deadhead some blooms here and there when your PeeGee first blooms.