Its probably what most people are suffering. It down to snow. If you have had alot sitting around for weeks then it has flattened the lawn, starved it of light and made it go blotchy. Give it some time to recover and when the weather warms it will soon sort itself out. abit later this month give it a rake to remove dead grass/thatch and then a feed to help it get over its winter flattening!

A picture would be good to double check as it may be something else!