Have you seen a mental health counselor for an evaluation? My first guess would be that you may have some degree of Asperger’s. I’d need to have a lengthy talk with you to be sure but many of your symptoms are common to people who are on the high end of ASD (autism spectrum disorders).
A second guess would be that there is something neurological going on. To determine if that is the case, it would be useful to have an evaluation by a neuropsychologist or a neurologist.
You’ve managed over 50 years of life in spite of these difficulties. For that reason, I doubt your symptoms are related to those of your niece. You may share some symptoms, but I don’t think you share a diagnosis. However, as I said, I’d need far more information to identify the problem. I hope you will consider seeing a professional for an evaluation. Such an evaluation could both ease your mind and provide some practical suggestions for overcoming some of your difficulties.
I wish you well.