Brownie,
Go to an opthalmologist. Most of the time, they can see inflammation in the optic nerve and can diagnose optic neuritis. If the Dr. doesn't see the inflammation but suspects ON, then they will order an MRI which will most definitely show ON. Remember that ON is not MS. Many people with MS develop optic neuritis but this condition can also stand alone.
Good luck, and I hope you are feeling better soon.