I agree with Bob. Generally fertilizer should last at least 4 weeks,
more likely 6. Did you put it down at the right rate? Too much
nitrogen can promote fungus and disease, so I wouldn't over do it.

One thing you could that would help it would be to aerate it. If it's
had heavy traffic, it's likely compacted. However, that should have
been done before the pre-emergent crabgrass preventer was put down. If
you don it now, it will at least diminish the effectiveness. Also,
have you tested the PH and adjusted? That can make a diff in how the
lawn responds to fertilizer.