Overwatering frequently causes problems with grass, but usually it is the homeowner who overdoes it! In this case Mother Nature turned the faucet on high (pardon me, couldn't resist). The best thing I can recommend is to apply a light foliar feed of seaweed and a product like Super-thrive to your lawn. Follow the directions carefully with Super-Thrive; you only need a very small amount. These products will feed the soil to make your grass healthier so it can withstand whatever is going on.
If you fertilized your lawn, and especially if you applied a Weed and Feed product, you could have stressed your new lawn sufficiently to make it vulnerable to attack. NEVER use Weed and Feed products! Most of them contain Atrazine, a toxic chemical proven dangerous to aquatic life. Florida residents are coming to realize that healthy ground water is essential to their state's future. The resulting raised consciousness has fueled the demand for native plants and organic products. Learn about organic products and how to use them at a nursery that promotes them. Good luck to you, and thanks for the question.