Auto-immune diseases are VERY hard to diagnose -- and they are elusive enough that very often Drs/patients aren't sure of the exact diagnosis until the symptoms respond to a course of treatment known to control disease.
Plaquenil is not going to hurt you - it's been in use for many years as an anti-malarial, and is known to inhibit progression of Lupus. (Some people do have upset stomach, but when taken with food that should go away after 7-10 days. )
MTX I might be more hesitant about
. Most Rheumies start with Plaquenil & Prednisone to get the inflammation under control, then once it's more managed use either Imuran, Cellcept, or MTX to keep it quiet. Auto-immune diseases manifest so differently from person-to-person that we don't really know how anyone is going to present symptoms, nor do we know what med might work for any individual.
Most likely your pain is coming from inflammation which is coming from an auto-immune disease. They are trying to address the disease with Plaquenil, and the inflammation with Prednisone, Imuran, Cellcept, MTX. Doing that will make the pain stop. Just taking pain meds for pain will not stop the underlying source! Ignore your instinct to stick to pain meds and let the Drs get to the root of the problem!!
Check out
https://www.lupus.org for more information. Diagnosis is by suffering from 4 of 11 symptoms, and how they respond to treatment. There is no ONE test that tells us what we have.
Many of us have trouble understanding the diagnosis & treatment process for these types of diseases. I hope I have helped you understand it. Let us know how it goes and/or with more questions.