It's probably breeding season, as Lord Sorril said ^ ^ ^ but could also be something else. Ever taken a fresh stool sample from him to the vet to be checked?
Hard to say about the size of the hides...most BPs like to feel snug in them, some so much so that they resemble tortoises when it lifts up over them.But
they also want hides that aren't too "open"- the doorway should be just big enough for the snake (with a meal bulge) to easily enter. You could try offering
something else just to test it before you run to get something else...even a cardboard box of the right dimensions (toss when dirty) to see if he uses it.