Randomly felt numb penis shaft and scrotum also have low libido. Urine/MRI came back normal. I'm 19, healthy, have eczema and been on steroid cream?

See Dr. Continue to see the Dr for your work up. The fact that the urine and MRI are normal are good sings, it may be more a topical issue form a dermatitis that could be affecting superficial nerves. The low libido is often psychological and therapy may help you. Best wishes.