I had shingles twenty years ago as diagnosed by my doctor. i had few burning red spots. now, same symptoms except no visible burning red spots on the outer skin. is it normal for no red spots to form? did shingles exist 100 years ago?

Rashes of shingles are always beginning with red spots then vesicles develop and they coalesce, rupture or dry off. Postherpectic neuralgia may have the same pain without rashes. My dad was born in 1914 and he knew about these painful rashes during his young age so I think this disease has been present for more than a century but its viral cause was just recently known with modern medicine.

Are the symptoms in the same location as they were 20 years ago? If so, you could be dealing with herpes simplex, not shingles. Shingles can occur without red spots or blisters, but that is unusual. Shingles has existed since antiquity. (The French called it "the band of roses from hell".) You really should see a dermatologist for a proper diagnosis and treatment.