What causes severe leg cramping and burning pain in both legs?

Hard to say: Potential issues include nerve entrapment, radiation from back, nutritional issues and hydration, metabolic and genetic issues like Charcot Marie tooth, vascular issues like poor circulation or poplite artery entrapment, exertional compartment syndrome, medial tibial stress syndrome, and stress fractures. Since the differential is so broad, probably should get checked by a sports doc