Hi Jeffrey

What type of soil are you using? Do you know the PH levels? (pH of six and seven should be fine)
Perhaps it has too much or too few nutrients. Do they change colour when they are starting to die?

When growing rosemary plants, provide them with well-drained, sandy soil and at least six to eight hours of sunlight. These plants thrive in warm, humid environments and cannot take extremely cold temperatures.

Rosemary prefers to remain somewhat on the dry side; therefore, terra cotta pots are a good choice when selecting suitable containers. These pots allow the plant to dry out faster. Thoroughly water rosemary plants when the soil is dry to the touch but allow the plants to dry out between watering intervals. Even indoors, rosemary plants will require lots of light, at least six hours, so place the plant in a suitable location free of drafts.

Dont forget to try some Rosemary as its said to enhance one’s memory :)