I always make a few draws prior to hunting. If I forget, I do it in the tree when I first get set. That limbers the old muscles up. Early in the morning, there doesn't seem to be as much strength in the ol shoulders and arms. If that doesn't help, I'd let off the bow weight a little. There could be other contributors, like eating something with sugar in it before you go hunting or too much carbohydrates. That stuff will zap your strength when you add excitement (insulin) too.