What Causes Severe Itching While On Morphine Medication?

Hi I take MSIR 30mg 4 x daily and its not working as well anymore and has started making me itch terribly, as in drawing blood!! I used to be on the fentanyl patch until I lost my insurance and cant afford $475 for a months supply. I recently put one i had left and had better relief and no itching. But what do i tell my dr and what will i test positive for? I have stage 1 pancreatic cancer, psoriatic arthritis, fibromyalgia and periphial neuropathy as well as severe panic anxiety disorder! Cant afford to lose my dr.