It is still early, you need to wait a bit longer before the real signs of flowering start.

I have quite a few, which were planted in Autumn, and none are ready to flower yet.

If you wait a bit longer, you should see signs of then getting ready to flower.

Or, if they are from previous years, then this is what often happens. Very few highly bred Tulips produce the same spectacular displays after the first year (although the species types do). One way to improve the flowering is to feed until late May, dig them up in June and store them, then replant in November.

I keep my garden fully fed throughout the year to keep everything in tip top condition. This is more expensive than other maintenance, but worth it.