I guess it would depend on how mature your lilacs are, though I would think that they should have bloomed by their second year.

Are your lilacs planted in full sunlight? Lilacs do best in full sun.

Have you been pruning them? If so, you may have cut off the buds which were forming for this year's bloom.

Lilacs. Prune right after blooming.

* takes off the dead flowers.
* plant doesn't put energy into seed.
* Next year's flower buds form soon after this year's blossoms finish.