Your Cereus should hve broad, leathery leaves with "somewhat" scalloped leaf edges. Where the scalloped edge dips into a V, you will see a little reddish bud. There may be several of these on a single leaf. These will grow into large pointed bufs with a "goose neck". When the bud shows white and the bloom tips are slightly spread, then it will bloom that night. It has been my experience that the grow you describe means it is doing well and I thin you should see buds soon. It has also been my experience that a pot bound (root bound) plant seems to bloom more often, As long as your plant is growing, I would not repot it. Feed it about once a month. Let me know when it blooms. Do you have it inside a greenhouse?

I have mine in a heavy clay pot with a heavy rock on one side because it leaning to the other side. Maybe you could find a heavy pot to put the pot you have into without repotting. Sometimes adding a little soil in this pot helps but make sure there is drainage. The original plant, not mine, is over 100 years old and has not been potting on for a long time. That one has support and it about 5 feet tall. It shouldn't bloom until at least Aug. I'm almost certain it wont do it until them unless there is some forcing involved with lighting. That's why it is a good moon garden plant. There are plenty of time lapse pictures on the web.