I have pain and stiffness in my hands, particularly the left one. The pain is mostly in the knuckles and back of the hand. Also 6 months ago.?

Possibly arthritis. Stiffness, pain, and swelling are the classic signs of arthritis. I recommend an evaluation by a rheumatologist or orthopedic surgeon. Examination and x-rays, and possibly blood tests may be necessary to confirm. Potential treatments include therapy, bracing or splinting, and arthritis medicines, such as nsaids, which include Ibuprofen and celebrex (celecoxib).
Rheumatoid Arthritis. If there is local swelling, about the knuckles and the extensor tendons, the case is stronger to suspect rheumatoid arthritis. Other collagen disorders need to be excluded. Proper referrals to an internist or rheumatologist are in order.