Lilacs are very low maintenance, you may be feeding it too much, they do not require huge amounts of nitrogen, but do benefit from potassium. That will cause lots of leaves and no blooms. Why are you pruning it? You are probably cutting off next year's blooms. It is only necessary to cut off spent blooms. Most lilacs take 3-6 years to show initial bloom, then it will only be spotty. It takes time.
Lilacs do not like wet feet, nor do they like drought. So watering would only be needed the first year of planting and during drought after that. Lilacs also require a certain amount of cold weather to put them in dormancy through the winter.
If your soil is fairly healthy, forego the fertilizing and pruning for a year and see what happens. Lilacs do not need a "companion" lilac.
