the pain might be caused by a pinched nerve at the spine.
another possibility is that the sciatic nerve is being pinched somewhere else by a muscle in spasm. for example the sciatic nerve passes thru the piriformis muscle in the butt. i just figured out my piriformis muscle has been in spasm/knotted for years (due to an earlier injury) which has been pinching the sciatic nerve.
i read about 'trigger point' therapy on the internet about 2 weeks ago and saw a massage therapist last week, and it looks promising. they try to relax the muscle so it doesn't pinch the nerve anymore. heres a related video:
How Does Massage Therapy Help Eliminate Muscle Knots? - YouTube
it sounds similar to mark's comments above.
maybe you got a charley horse/muscle spasm from the motorcycle trip, and its pressing on the nerve.