I also have snakes fasting. It happens, the weight seems fine actually my older male is not far away from your 1800gm to 1580gm in three months. The big question is do they behave normally and still have good muscle tone. Are there any unusual defections of large amounts of urinates. Basically do they seem the same just not eating? Check the husbandry and wait him out. Not having seen internal parasites I don't know what to look for but from what I have read there is usually a sign in the deification. Although if your is like mine he has stopped doing that a week or so after his last meal. I have been going by if the look healthy act healthy and nothing is out of the ordinary they likely are healthy. Lets hope yours and mine start soon.
Alex