If it prefers acid soil, then a fertilizer for acid-loving plants should be good. Look for something that says "Azalea, Camellia and Rhododendron" or something like that.
Perhaps next spring put it out where it will get more sun than it has had before. Now that it is well established in its pot, it should be able to take more sun and that should help it bloom. Morning sun is always preferable for these type of plants.
