Having lawn grass turn yellow is frustrating.   Lawns need quite a bit of care.  Fertilizer is important, but should only be applied when the plants are actively growing, and can use it.   It may be that applying fertilizer in January when the grass isn't using it caused fertilizer burn.  This year has been such a strange weather year.  Normally, we get so much rain, so often that any excess fertilizer usually just washes away.  This year we've had so much dry sunny weather that the fertilizer stays on the surface and can actually burn the grass.  This article on "Practical Lawn Care for Western Oregon" has good information on lawn care, from when to fertilize, mow, water, thatch etc. https://catalog.extension.oregonstate.edu/files/project/pdf/ec1521.pdf . Just click on the link.