Why does my thigh and knee go numb when i lay down? also have intermittent pain in rectum, back and tingling in bottom when i sit

Pain and numbness: I would highly recommend that you see a spine doctor, and probably get an MRI. Your symptoms are indicative of a spinal disease- herniated disc or spinal stenosis or some other nerve compromise. Please see a neurologist right away

Numb Knee: This could stem from a spinal condition (disc herniation, degeneration), sciatic nerve impingement from taut piriformis muscle, or many other structures or anomalies - Not enough info. Nerves leave spine in roots trunks chords divisions from spine called the lumbar plexus, and here L4-5, S-1 impingement of nerve plexus traveling on down. An MRI may reveal info. Check this with your doc-