My veins sometimes feel like they are burning. this occurs in various parts of my body and occurs sporadically. why?

Burning: Normal veins don't cause this symptom. It is more likely due to periodic irritability of superficial nerves in the skin and would be a type of neuropathy. If the symptoms are quite noticeable and frequent, get checked for deficiencies of calcium, magnesium, iron, b12, for elevated blood sugar and your thyroid status. Discuss this with your physician.