I have a honduran milksnake that was rescued from the animal shelter, where they were keeping them on cedar. The oil fumes damaged his insides to the point where I have to feed him smaller than normal meals all the time. If I give him two very small food items at a time, he will regurge. I know that a lot of the other snakes from this particular rescue (it was a long story, confiscated snakes and all), ended up dying after they went to live with other people, because of the oil fumes. I am not saying that this is definitely a problem for you because it is pine, not cedar, but there have been definite reports of pine oils causing problems in snakes. Why risk it?
I would suggest that you take the snake off the pine, put him on a paper towel substrate, then wait for two weeks after the last regurge, try a small meal at that point. If he eats it, then wait another 10 days and try again. DO NOT HANDLE HIM AT ALL during this time! DO NOT DISTURB HIM by going to peek in his cage, other than to check for regurge mouse. If the snake is in his hide, do not pick up the hide to check him. If he has regurged in there, you will be able to smell it without any problem.
Make sure that your temp are accurate. Do not measure the temperature by using a stick on type thermometer. Get a good digital thermometer, you can buy one for $15 from Radio Shack. Measure down on the substrate, directly over the hot spot and on the cold spot, also. The temps on the hot spot can be significantly higher then up on the side of the cage.
Just my opinion.
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sue