Yes, I'm not too far from you, just south of Chattanooga. It was a very difficult season last year, super hot and dry.
Are you sure your watermelons were fully ripe when picked?
Other than that, the weather we had may have been the main culprit. All that watering that we had to do (I was watering almost every day also), flushes nutrients out of the soil. Manure, compost, etc are all good stuff, but not very concentrated nutrients (NPK around 1-1-1 or less) and the nutrients aren't available to the plants until the compost (etc) breaks down more. In the situation of having to pour water through the soil every day, you probably needed to be fertilizing more, with something more concentrated than compost.