It can appear in any part/s of the body or all of your body.
I can't believe that doctor told you it could not be SFN because you didn't have pain in any one specific place.
Mine was in my upper body before it spread like wildfire to my whole body. You need a new doc. Do you have episodes of numbness, tingling, wet drops, shooting/ throbbing pain?
Some of the doctors aren't schooled on non length dependent SFN. They look for the typical stocking and glove pattern which is more common.

The only problem is, you already have the meds so there isn't much they can do about it except give you name for it.
Have you had a spinal tap, autoimmune blood work up, full body/ brain MRI? Have you been heavy metal tested? Have you had a work up of vitamin/ minerals?