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?

Low libido: If you have not yet had your gonads examined and evaluated you must see your doctor soon. Healthy at 19 but with low libido requires careful examination.

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.