it needs more fert man. it has been too long especially for a cheaper starter fert to last this long and with plenty or water to leach the minerals away. needs fert. one other thing is the colder temps can do this especially where soil structure differs from area to area in a lawn, new or not. more than that i still think it is fert without diagnosing on site
all is fair in love and grass!
Man, it smells like sheet, do you smell that!!