I Was Taking 30 Mg Opana Cr 2 X Per

I was taking 30 mg Opana Cr 2 x per day and 30 mg oxycodone ir 4/day. Pharmacy will no longer fill this combination of medication and insists I take 20 mg Opana cr 4*/day and 20 mg oxycodone hci instead. I seem to be having a problem with taking these in this combination. It does not relieve the pain and for some reason I am itching like crazy. Is there a reason why I should be forced to change my medication?