Photoshop does not provide an easy mechanism for sequentially labelling layers.
Download this script, select the layers you want labeled sequentially, and run the script.
The script will provide you with a single prompt allowing you to type in a prefix, type in a suffix, decide whether you want to pad the numbers and by how much, enter what number you want to start counting at, decide whether you are incrementing or decrementing, and choose the layer direction (bottom to top or top to bottom) to traverse through the layers.