I've kept my amaryllis growing since...

The bulb needs to go through a dormant period. Ideally, you would taper off watering in September, then store the bulb dry in a cool, frost-free place for 60 to 90 days. At the end of the dormant period, replace the top one to two inches of soil with compost. Water thoroughly and bring the pot to room temperature. Your amaryllis should bloom in six to eight weeks.