Unable to use pain relief.

After being misdiagnosed with fibromyalgia for 12 years, I saw a private consultant last year after being taken into hospital, not for the overwhelming pain of a flare up, but due to the fact that the pain had sent my heart rate soaring.
He sent an urgent referral back to the UK NHS, after diagnosis of Psoriatic Arthritis, as I should not have to pay for treatment.
Since then, I have been seeing a Rheumatologist and am on Methotrexate & physiotherapy.
However, the misdiagnosis of fibromyalgia led to treatment with Gabapentin, my doctor giving me an excessive dosage, leading to the acute ward in hospital where I was diagnosed with Chronic Erosive Gastritis, my stomach is permanently damaged.
Unfortunately, this means I am unable to take any pain medication at all.
I have PSA in 12 + joints and awaiting an MRI for my spine and pelvis for spondyloarthritis.
Please can anyone advise, anything I read everyone is on pain medication, this is not an option for me.