Since being diagnosed with RA, I have trouble concentrating and remembering things. Is this normal and to what extent will it become debilitating?

You can review symptoms of RA: https://www.empowher.com/condition/rheumatoid-arthritis/symptoms, but loss of memory, difficulty concentrating are not symptoms of RA.

Please review the patient information brochure that comes with your prescription for side effects; here are the side effects listed online for hydroxychloroquine (accessed at National Institutes of Health (NIH). Tell your doctor if any of these symptoms are severe or do not go away:
* headache
* dizziness
* loss of appetite
* nausea
* diarrhea
* stomach pain
* vomiting
* skin rash

If you experience any of the following symptoms, call your doctor immediately:
* reading or seeing difficulties (words, letters, or parts of objects missing)
* sensitivity to light
* blurred distance vision
* seeing light flashes or streaks
* difficulty hearing
* ringing in ears
* muscle weakness
* bleeding or bruising of the skin
* bleaching or loss of hair
* mood or mental changes
* irregular heartbeat
* drowsiness
* convulsions

Since you are experiencing "mental changes", it is important to contact your doctor and let him/her know that this is a side effect you are experiencing from the medication.

Another possible cause is that you may be feeling distracted or worried / pre-occupied by your diagnosis and symptoms. Do you feel overwhelmed or particularly sad about your diagnosis, or do you feel the mental changes you are feeling are a result of your medication?