If you are a lefty, some sort of repetitive motion may be to blame. Pay attention to whether it hurts when you start doing any repetitive thing.
Do you spend a lot of time on your phone, the computer, or writing? To me, these symptoms sound like carple tunnle, and these things can cause just that. I'm no neurologist, so I would suggest that you talk to a professional before making a decision. Usually, treatment would be wearing a brace (if the pain is really bad), spending less time doing those activities that cause the pain, or---in an extreme situation---surgery.
I hope this helps!