When plants don’t bloom, there's usually a laundry list of possibilities. In the case of an evergreen azalea growing in a container, these include too much shade, an excess of nitrogen fertilizer (which results in much plant growth at the expense of bloom), deer or rabbits, and a late spring frost or cold spell that killed the buds. But the two most likely causes are drought (or too little watering) the previous summer, when the flower buds are formed, and the plant being potbound (the roots forming an impenetrable mass in the container).
You don’t mention what size container the plant is growing in. If it’s the same one you bought it in, it’s certain to need repotting after three years.
To be sure, remove the plant from the pot and check the roots. Or look at the hole at the bottom of the pot – can you see roots growing out there? If so, it’s time to replant - either in a bigger container or in the ground (since you live in a region where azaleas thrive outside).
Azaleas like acid soil that’s moist but well-drained. It should be loose and crumbly. For a container, you can mix up your own, if you like: Use half commercial potting mix made with peat moss and half fine pine bark.
Have the soil mixture thoroughly soaked through before you plant. Then remove the azalea from its pot and tease the matted roots so the ends are loosened from the ball several inches. This will allow the roots to grow out into the new soil. (If you don’t loosen the roots when repotting, they often just keep growing around the around as they were, and your problem continues.)
Place the azalea at the same depth that it grew before or just slightly higher. (Never deeper.) Add 1 inch of mulch over the top of the soil. Then place in partial (not deep) shade.
Fertilize once with an azalea-camellia fertilizer and water when needed to keep the soil from drying out.
Spring is the best time for replanting. When planting in the yard, choose a spot with partial shade and loose, acid soil that can be kept moist.