Optic neuritis followed by hypersensitive skin (leg then trunk) and aching arm, could it be anything else besides ms?

Possible: First, the subsequent clinically definite diagnosis of ms occurs up to 50% of the time after optic neuritis. Secondly, the sensitivity and aching may or may not represent spinal cord or allodynia issues, and could be associated with peripheral nerve disease. Third, an MRI of both neck and brain could be reassuring, and a negative spinal fluid would also rule out ms at this point. See neurology.

Yes: In addition to multiple sclerosis as a cause for optic neuritis and unusual neurologic symptoms, there is a separate diagnosis called devic's syndrome or neuromyelitis optica (nmo) which can cause both optic neuritis and a separate demyelinating disease called transverse myelitis. I would make certain you are seeing a neurologist with skill in neuroimmunology/ms to make certain of your diagnosis.