There are many possibilities, Carla. May I ask you some questions?

How much water do you provide the plant when watering and how often do you water?

If you insert a finger into the soil to a depth of 3-4 inches right now, does it feel dry, almost dry, moist or wet?

How many hours of sun does the shrub get? Can you also approximate from what time of the day to what time of the day?

Are the yellowed leaves concentrated mostly on the bottom of the shrub? The top of the shrub? Randomly scattered throughout the shrub?

If you look under the leaves, do you notice any insects or damage that could be attributed to insects?

Have you or someone in the household sprayed chemicals nearby recently?

Have you ever had a soil test done? Are any other nearby shrubs affected?

Luis