I may soon be on morphine.But my skin itches and crawls when i've had it in the hospital. Need to use it. HLP?

I've been on many other narcotics. Doc. just wants to find something equal and won't go up on the meds I've had which is kind of crazy in my mind. I took methadone and percocet for over 4 years and never changed the dosages! Also the only morphine I've had has been interveously in the hospital. Would something like benadryl help? i would love to hear all answers?