This is very common in young greens and is often nothing to worry about. Was it eating prior to you getting it? Was it a reliable breeder? My green has gone of feed for up to 4 months. Young greens have a very slow metabolism compared to say a retic. This allows them to go off feed for a quite a bit longer safely. What are your heat levels? If you offer a larger water tub what is the temp of the water? Try not to handle the snake unless needed for a little while, and be sure you offer a hide.

Keep us posted,
Ed