If you're using potting soil, your plant probably doesn't need much of it. CC's are jungle epiphytes, similar to orchids. They do like to stay moist, but need tons of air around the roots also. In a pot of potting soil, which has very little air in it due to the tiny size of its' particles, the roots will probably be in a sphere around the sides and bottom of the pot, where there's oxygen available. Using a more chunky/porous/airy soil can help, and unglazed clay pots that can breathe.
Your plant is probably Schlumbergera truncata:
Christmas Cactus (Schlumbergera truncata)
The info here is excellent: