Lilac bush will not bloom. 4 years old; 2 blooms. Not enough sun?

Mine is of similar age and about 3 feet tall. Two blooms this year and I was happy with that. Here is a site with overall care for lilacs:

https://www.almanac.com/plant/lilacs

Not enough age. Lilacs bloom between 5 and 7 years old. Let it mature another year and you'll probably get blooms galore.

Age is a factor but so is sun. I would wait 2 more years an kepp an eye on how much sun the plant gets during that time.

Mine bloomed after adding some lime to the soil get it at home depot ot Loews & read the directions good luck

Possibly too much shade also if extreme acid soil , not good , won't hurt to add lime . If you fertilize don't go too heavy on Nitrogen .

Almanac.com web site suggests planting deep . DON'T do this , planting anything too deep or mulching higher than nursery height is most common cause of plant death ! Rots stem/trunk ! Landscapers are the most guilty by adding 2" of new mulch annually !

We have 4 of them, we use epsins in salts around the base in the spring. And we cut the suckers off the base at the same time, and have gotten so many blooms. We also use it around our plants and it's tons cheaper than miracle grow. Good luck