There are spots that appears on & off on my tongue what is that ?

Tongue spots: You may have a condition that is completely harmless called "geographic tongue". If is comes and goes don't worry about it. If they are white and burn it may be thrush(candida) and may need a prescription to correct. If the spots are ulcerations or painful you should see an ENT for evaluation and possible biopsy.

Spots on tongue: The spots are irritated, elongated taste buds. Many irritants, specifically reflux of stomach acid, may be associated with irritated taste buds. Sometimes, the tongue looks like a MAP = geographic tongue. A yeast infection may also look this way, typically following recent use of antibiotics.

Geographic tongue?: See: http://www.mayoclinic.org/diseases-conditions/geographic-tongue/basics/definition/con-20027435 See your own dentist to confirm this guess as there are other possibilities that might require treatment.

Migratory glossitis: also called geographic tongue. is a benign condition that has been associated with emotional stress, allergies, diabetes and hormonal factors. If concerned see your dentist for evaluation. Good luck.