Stress opens up a whole basket of potential issues. It can be the catalyst for a weakened immune system which can invite disease, or a shutdown in feeding. Stress coupled with improper husbandry is a bad combination.
Most issues, unless glaringly severe can be handled "in house" by providing a perfect setup.
Vet visits, unless absolutely necessary add to stress and drain your pocket$. If there is a big issue, by all means go see a vet, but the constant poking and prodding is compounding any issues you may have. Don't relieve your stress by causing the snake more stress.
I may have missed the key issue/problem here but I read back and didn't see it.
Royal pythons are secretive, and solitary. Having one and expecting to be entertained by an active, outgoing snake will be disappointing.
You have to let them do what they have evolved to do. They are pre-programmed for self preservation and they accomplish that by being hidden and secretive, especially when young. They don't want to be checked on constantly.
I've learned as much as I can about ball pythons in a whole, it's just the whole sickness thing with them is tricky
Again, I seemed to have missed the "sickness" part here but if you have truly learned all you can, you need to take a breath, relax and go back and see what makes them comfortable. Don't let your anxiety transfer to the snake. There is a way to love something to death. Don't let worries that aren't real creep into your head.
A hidden royal is a happy royal/ball.
I apologize if I missed the actual issue, but from what I've read here "stress" was the topic?