Vets for herps are a bit like antibiotics for herps...make SURE you really NEED them before you use them.The thing is, they mean
well but their training is mostly MEDICAL, not basic husbandry that you might assume they'd be up on. So things like the pink belly- yes
it can be a sign of "septic" /infection, or a "burn" from excessive heat (UTH), but in BPs it's pretty typical for oncoming shed too. (I'd
be checking his eyes in a dark room with a mini flashlight, shine across the arc of his eye & if a shed is coming it should look a bit milky.)
Slight whistle without other symptoms aren't that rare when snake is in shed...but I applaud your good motives, sorry it didn't go well.