Pain medication allergy

I have terminal TNBC met to the liver and other areas in my abdomen and for the past 2 years ive been ok, yes the chemo is brutal every week but ive felt fine. This last month or so ive had nothing but pain, like everything has come at once. My whole torso hurts especially if i lie down and my shoulders are painful most days and the last day my legs and feet have  began to swell. 
Im allergic to opioids after being in hospice back in 2013 for spinal tumour pain management we found all i can tolerate is methadone i cant take any gabapentin pre gabs morphine anything at all. My worry is this pain will worsen as the cancer progresses so how do we control it?