I just looked at the photo you posted of the snake, its not skinny, its healthy. I am posting two pics. First is my almost 3 year old corn who is between 3 and 4 feet long and is healthy, the second is the 13 year old corn I recently took in that is FAT. Hope these pics help you feel good about how your snake looks. Personally I would feed one mouse every week or two, my healthy guy gets one adult mouse every 2 weeks because being fed every 7 days or even every 10 he was getting round.