How are you taking the temperatures? What is the cool side temp.? If your thermometer is not accurate, he might be over-heating? His behavior suggests he's uncomfortable. Might try dropping the 90* to 88*? What kind of heat is being used? Is it controlled by thermostat? You do understand, I hope, that you cannot just set a t-stat to a temperature without double-checking what it really is in the snake's enclosure- otherwise it might be higher if the heat is building up.
Any unusual stools lately? Did they actually do a fecal exam on a fresh stool sample? If not, get it done A.S.A.P. as he might also be having internal discomfort.
How's his appetite? How's his weight? What's his age & how long have you owned him? What is his weight & what size rodents are you feeding him & how often?
I ask because every once in a while we find someone that is drastically underfeeding their snake. His behavior could also be hunger. Remember that his metabolism is controlled by the temperature- in warm weather, snakes digest faster & often want to eat more.