You did not mention what type of heat you are using. I prefer belly heat for retics. I am going to get bashed for this but I keep my hot side at 100 F. Say what you will, there is nothing that will change my mind on the higher then normal temps. My retics are healthy and have been for close to 7 years. What I am trying to get at is raising your temps above what you have them set at. If you are using a bulb, I'd switch to a Flexwatt type heater. Make sure you have a way to regulate the heater or your temps will get much higher then 100 F. Where is your thermometer located? Are you sure of the temps?
You say the retic is 7 months old and you are feeding it mice? At 7 months a retic should be eating much larger prey items. Hatchling retics can eat adult mice or small rats. Looking back at some of my records at 7 months my retics were eating rats between 400 - 500 grams in total weight every 7 days. Most of the rats were around 200 grams each at that time. Your average large adult mouse is in the area of 30 - 35 grams. You do the math.
Is your snake defecation on a regular basis? This can be another reason the snake is not eating. If the snake is not having regular bowel movements there could be a blockage. Though it is not common it happens.
Lastly how familiar is your vet with reptiles? A good reptile vet is hard to find. Your average dog & cat vet knows nothing about reptiles. Ask at your local pet stores of a good reptile vet. If you live near a large city most have local herp society. Go to a meeting and ask around. You would be surprised how many reptile vets are members of a herp society.
These are just a few thoughts that come to mind. I wish you luck.
Jim