
The MTX dose for autoimmune disease is about 1/1000 the dose they use in cancer patients. MTX also has a long clinical history, which makes it a trustworthy drug, they'll be no "surprise" side effects.
All immunosuppressant medications increase your risk of infection.
Still, MTX does have side effects - doesn't mean you personally have any of them, a few lucky ones get away scot free

- but most folks have some trouble at least at the beginning of treatment: nausea, stomach troubles, hair shedding (mild to moderate hair loss that grows back, Plaquenil can cause this too, but having any chronic inflammatory condition can cause hair shedding), anemia (again, any chronic inflammatory condition can also cause anemia) and fatigue. You can take what's called a "methotrexate rescue", a drug that binds to MTX in your blood and sweeps the unused MTX out of your system. It's this MTX that "hangs around" that causes most of the side effects. The rescue drugs are Leucovorin or simple high dose folic acid supplements.
My question would be, how well is Plaq working for you?
If you do continue taking Plaquenil, you'll need to have your eyes checked on a regular basis (every 6 months to a year) to avoid a
rare side effect that can damage your vision.