I have some Vinca at my house that seems to thrive in the shade and once it grows out into the sun it's not happy, it turns around and grows back to the shade.
Maybe you could plant a few trees around to provide some shade.
Watering is tricky. How often depends on soils and other factors, but basically you want to let the soil just dry out before watering again. If it stays constantly wet, you can mess up the soil gas exchange and promote fungus problems. Pull the mulch back and poke your finger into the soil to get an idea of how wet things are.