Why Is My Toe Turning Purple 2 Months After A Ingrown Toe Nail Surgery?

It sounds as if the blood flow is restricted in some way when you are sitting. If you have not been to a different doctor I would recommend getting in to see another one to get a second opinion.
If you live near a medical college I am sure that they would love to see you and address the problem as a learning experience for their students. You will find some of the best doctors at medical colleges.

It sound like it might be a nerve problem!!!!! Or an infection  under the skin. See the foot specialist.  good luck! You might have also gout. You really need to see the specialist!

It is because your toe has no blood circulation.