One prominent superficial vein on left leg, pain radiating up whole leg constantly burning pain. dvt ruled out. would sv cause this pain? crps? other?

Pain: Superficial thrombophlebitis is still possible. There are more possibilities not all vascular. Keep working with your doc to find the cause.

Sciatica?: Unlikely to be vascular given symptoms. Seems like you're describing a radicular pain pattern ie sciatica. Could be a pinched nerve in the spine. If recommend you see a physician to be worked up appropriately.

Possibilities: If you have a superficial venous thrombosis you can certainly have significant pain, but it is usually associated with redness, swelling, and warmth over the affected vein. Burning pain often has a neurogenic origin. Crps (also called reflex sympathetic dystrophy) could be a possibillity but is typically associated with having had an injury of some kind (including surgery). See your doctor.