Anyone have any leads on why my index finger could suddenly experience some kind of weakness?

I know the rules says no medical advice, I'll do my own research and followups (and see a doc soon) but it's not possible at the moment hence the question for my own peace of mind:

I've been having some kind of muscle ache on my neck and right side rhomboid (upper back) for months now, it was particularly bad today. and suddenly I noticed I'm experiencing some kind of weakness in my left arm, specifically when using my index finger.

Anyone experienced this before or have any leads I can look into? (I've already searched and found a myriad of spinal and muscle related issues with symptoms but it doesn't seem to match)