Here is what you need to do if you have not done already
Get a 6 quart tub, put some aspen bedding in, you can add a 6 inches plastic flower pot saucer too for added security, provide a hot spot of 88 degrees, wait a week, and offer a live hopper mouse.
All those are KEYS to start a new hatchling out of the egg or stubborn young feeders.
The important thing are SECURITY and keep it warm.
In the mean time NO HANDLING.
A vet will not help what you need to do is get the animal to eat on it's own and if all fails even after what I suggested at some point assist feeding will be required.