Pain in hand, knee and writing problem.

I am suffering from an unknown disease (for me). Everything starts 4 years back. I was uncomfortable in during writing My handwriting gets degraded with time. I am getting mild pain while writing. For this problem, I meet with a neurologist. He said that you may be suffering from writer cramp. He thought this is the problem related to my mind and suggested MRI of my head. MRI report does not show any problem. He started medicine​ of writer cramp. I have taken these medicines for around one year. But I do not feel more improvement. With time I also suffering from mild knee pain. While typing on mobile, I am getting numbness and pain in my hand and figures joints. After that, I met ortho doctor. He advises X-Ray of my knee and blood test. In x-ray no arthritis​ detected. Then I have taken tablets of B12 and D. With time deficiency of B12 and D gets resolved but other problem like pain in hand and figures joints, problem in writing, knee pains remain. Advice probable disease and doctor.