Go to your GP. Blood tests will show rheumatoid arthritis. You can address it with dietary changes and supplements, it doesn't have to get really bad. You are still young enough to head it off. Boost your immune system as much as possible and please avoid steroids. I know Prednisolone is commonly prescribed but at your stage, if it is RA, I wouldn't take them.
Apart from from go to your GP please ignore EVERYTHING in this post. If it is RA then it is an autoimmune disease. You CANNOT 'boost your immunity' if your immunity is low yes it can be increased to normal, an immune system that has started attacking your body does not need boosting, eve if it was possible.
Get to your GP and get a referral both to Rheumatology and to a physio.
I have psoriatic arthropothy, diagnosed at 26. There is a lot that can be done.
When I had fingers as you describe I was told to put a wad of cotton wool in my palm so that the fingers can't get into the cramped position.
Whilst I was doing this I had 'resting splints' made, these are solid plastic molded to my hand's in a resting position, when my hands are bad I wear them for 1 hour a day.
If you are offered a steroid jab take it, I'm lucky in that 2 of the GPs at my local surgery do them and I don't need to go to the hospital.
I was on methotrexate for years but I never got rid of the side effects so I opted to give up and I use pain killers and anti inflammatory meds.
I do have all the tools to help do buttons but I tend to buy clothes I van put over my head.
There are a lot of different treatments and assuming it is RA then you need to make a plan with the professionals that suits you and our lifestyle.