Answer: Based on your description it is difficult to make a definite diagnosis, but it is possible that the plant is being overwatered. The soil should be slightly moist but not sopping wet, and during cool weather the soil will actually stay moist longer than it would during hot weather -- a shady location will also help it stay moister longer. You might want to check the soil with your fingers, reaching down below the surface, and see what is happening there.
Since it is a newly purchased plant, you might also want to consult with the nursery where you bought it and see if they can be of any assistance. I'm sorry I can't be more specific.
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