The new growth this year could already be showing bud for next year. Have a look. It's the summer's growth that produces the flower so it sounds as though you're on the right track. However, lack of water at the roots now will have a serious effect on the plant's capability to produce flowering growth. Is it potted or in the ground? Potted, it may need a proper rejuvenation, either by a prune and feed, a re-pot, or at least a top-dress of good stuff. Perhaps moving to a shadier spot? Sometimes feed just isn't enough. In the ground, all other things being equal, I'd only suspect dryness at the roots at the critical time. Unusually for Wimbledon week we're nice and sunny, so your rhodo will need support, just like Andy Murray!