You have probably already identified the problem: soil compaction. Compaction is troublesome in new landscapes where heavy equipment has been used during construction. Aeration is definitely the cure. All the water and fertilizer in the world are little use if the grass fails to get its roots into the ground. Most grasses are pretty tough, so you can make three or four passes (not just two) with the core aerator, a minimum of once a year (twice is even better).