Since this has been going on for quite a while, I would definitely recommend that you go see your primary care doctor
for an evaluation and some initial advice.
Based on your description of what is going on, I think that your intuition may very well be correct, and this may be related to some sort of repetitive use or strain injury
from working so hard with your hands all the time. Tendonitis, which is an inflammation around the tendons in the fingers, is a relatively common problem and could definitely give the symptoms you are describing. It is not uncommon for this pain to be worse at night, because this is at the end of your day of work, when the strain is most pronounced.
It is important, however, to rule out any other more serious problems, such as an infection in the joint or finger, or an arthritis
. Your primary care doctor should be able to figure all of this out with a simple physical examination and, perhaps, some blood work or x-rays.
If your doctor does think this is just a strain injury, then they will likely prescribe some anti inflammatory medications, and they may also recommend splinting the finger.