who am I?

I've got gloves on my hand And a patient to tend But these poems on my mind Like an author with his pen But I'm yet to prescribe And I'm the doctor, but I'm sad Like an author goes bad, with a comic that is tragic And then I will sing me the twinkle twinkle little star And then wonder what am I? Dress in a scrub and a lab coat Or in a vest with a pen at a table Or maybe I'm like a diamond found in the sky