Hello @petluv17, Welcome to Connect. I did a search of Connect and wasn't able to find another post by a member discussing blue fingernails as a side effect of gabapentin. I'm wondering if the blue fingernails might be due to something else since you have taken gabapentin for many years before the symptoms occurred. It can also be caused by a low level or lack of oxygen circulating in your blood. Here's some information on possible causes:

-- Why Are My Fingernails Blue?:
https://www.healthline.com/health/blue-fingernails
You mentioned the doctors do not know what is causing it. Are you able to seek a second opinion or possibly seek help at a teaching hospital or major health facility?