do you prune it? if so that is usually the cause of lack of flowers.

The general advice is:

'It is not necessary to prune rock roses at all. You may however choose to do so to improve and encourage a bushy habit. Pinch back the sappy new growth after flowering to achieve this.

Cistus, particularly when mature, dislike being pruned back hard to the older wood and can often respond by dying. Older, leggy plants are best replaced rather than pruned as they will seldom respond with new growth'.