Certified GKH Gardening Expert
You may not be watering it enough. You need to make sure that the water gets all the way through the soil. If the soil is very dry, it may actually start to repel water. So enough water for another plant would not be enough to rehydrate this one. Give the soil a good, deep soaking at least once a week (in addition to regular watering) and that should insure that it gets enough water.