Hello there. I'm sorry you are experiencing this! So, Rheumatoid Arthritis is an autoimmune and inflammatory disorder. A person with RA's immune system attacks healthy cells by mistake causing pain and inflammation (swelling). It's progressive but for most people would involve more than just one joint, one finger. Most often, many joints are affected. It's more common in women, but men 'can' get it as well. It usually has 'flares' in which symptoms are worse. There are other symptoms of RA too such as fatigue, warm joints that swell most often in the joints closest to your hand, possibly fever. Probably weight loss. Other issues of an inflammatory disease are things like red eyes, dry eyes, mouth dryness, rheumatoid nodules or lumps in the skin over bony areas, etc.
Now, one joint having an issue should not be the strict basis of this rather serious diagnosis. Have they done blood work? That should be ordered for you. Blood tests look for antibodies, inflammation and anemia to diagnose. Normally x rays are taken as well to check progression.
This slide show with pictures may help you. https://www.webmd.com/rheumatoid-arthritis/ss/slideshow-ra-overview Now, most definitely, RA can start by involving or affecting a single joint. Absolutely this is the case that it can happen. And it also usually starts in the hand.
Here's another overview of RA. https://www.mayoclinic.org/diseases-conditions/rheumatoid-arthritis/symptoms-causes/syc-20353648
You need an ESR or sed rate test, a C reactive protein test (your doctor may choose between these if they don't give them both to you), and other common blood tests look for rheumatoid factor and anti-cyclic citrullinated peptide (anti-CCP) antibodies. So, you need to do this and get some imaging done to have a diagnosis.
Naproxen is pretty common to use and wouldn't hurt you if you didn't have RA but you need a proper diagnosis! Nsaids help and are often used early on. But as RA progresses, other things are often also used like Disease Modifying antirheumatic drugs called DMARDS, steriods and biologic agents.
So, not sure if that answers your question. But yes, one joint isn't common for long with RA but not uncommon in the beginning.
I have RA, and it started in one toe, then later one finger, but when in the finger it affected the whole hand, couldn't even have a drop of water running on my skin. Mostly just in one side, until meds where it started showing on both sides.
THAT SAID; You don't nessecarily have RA because of one swollen finger, that reoccures. And I really hope that it's not the case for you, as I wish you a better life than this.
There is a few things you can do yourself to check;
Notice what you do every day -playing games, using the finger more on f.ex the screen, mouse, etc. If you play that is, or on other things if that is the case.
Try to avoid what you do the most, or switch finger you use (takes a bit time to get used to), to see if it can help.
Also try, if you drink sodas or other heavily sweetened beverages, to cut down, or even avoid that, and other sugary stuff for a week, (just to see if you get improvement), it usually help a great deal if RA, but also other inflammations.
Try to avoid red meat, or foods heavily refined.
I found that most of the inflammations in my wrists came after I got an ipad, etc. But also from repetive movements can also trigger inflammation.
The most pain and inflammation relief, I've gotten, is from quitting sugary things and adjusting my diet, finding substitues for white sugar (f.eks maple, agave, honey, dates, which I use in recipes instead). You can also look into anti-inflammatory foods, like walnuts, cayenne, olive oil, etc. But make sure when on meds like naproxen, that you check with a pharmacist if it goes together, as som can increase or decrease the effect...+ naproxen is not safe to use in the length.
Have they taken a blood sample called rheumatoid/revmatic factor of you? If that is normal, it may be something else, as it's usually is very high if RA. Or does anyone close related to you have it?
I really hope you figure out of it, and that it's not RA. :)
Anyhow the change in diet and habits can prevent a lot of things, and keep it in bay too, (not saying you eat bad, I've no idea), so worth a try anyhow.
Feel free to ask if you have questions. :)