Unless you have a history of significant injury
to the thumb in the past, arthritis
of the thumb would be very unusual at your age, although in older people it is a very common problem.
More likely would be a tendonitis of the thumb, called De Quervain's tendonitis. This commonly occurs when the thumb and the tendons in the thumb are subjected to repetitive motions and stress, usually from common everyday activities involving grasping objects with the thumb. When the tendons become inflamed, these grasping motions can become quite painful.
Treatment for De Quervain's tendonitis is usually conservative, meaning rest, ice, and antiinflammatory medications like ibuprofen are the first line of treatment. It is also important to specifically avoid if possible the activities that bring on the pain. Occasionally, a thumb and wrist splint can be helpful for avoiding further strain.
If these measures do not work, there are additional things that can be tried, including injecting medications into the tendon area to reduce inflammation.
First, you should talk with your primary care doctor
. They will be able to confirm a diagnosis after performing an examination of your wrist and hand. They will also help you decide which is the best treatment for your case.