ah, its in a pot. How long's it been in the same pot? This is a large shrub and will rather quickly outgrow its container, so should be potted on every year or so till its in something about 18 inches deep by 12 inches wide. Pruning after flowering is critical too for pot culture. The symptoms you describe sound like a problem with drought - if your plant is potbound, there's not enough soil left to retain any moisture for the plant to use.