Snakes go off food for several reasons: Stress, sickness, or breeding, (and some may fast over the course of the winter). So you have to evaluate your husbandry, etc.
Have you had the male tested for internal parasites? Does he have at least two snug-fitting hides? What are your temps at? Are they housed together (snakes may go off feed as a result of being housed together if they are stressed by the other/s)? Does this snake get handled frequently (another stressing factor)? What kind of feeding strategies have you tried?
For substrate, shredded aspen is good, newspaper or papertowel also work well.
I am not up to par on my colubrids, so I cannot coment on breeding size
Good luck