What Could Cause Bicep Soreness?

Dear Doctors, I am a 51 yo white male who has been in great health all my life. Last May I began to notice that my left bicept was very sore for no reason. I don t recall exerting myself or over using it. I also noticed that my briefcase and luggage seems heavier than normal in both arms and I had to often switch hands. A few week later my right bicep was aching too especially when using it for every day lifting activities. My primary care doctor though it might be tendonitis and put me on an NSAID that did notthing. A few months later both forearms also have become very sore and painful when in use. I feel like I have become quite week in both arms having pain and weakness while doing things like raking leaves and using a screw driver. over the past few months my wrists and fingers in both hands have also become sore and weak. And things like carrting wood in the house for a fire is difficult but I can still do it. I went to a neurologist who could not detect any weakness or a cause. My legs seem fine , perhaps a little sluggish, but I can still go out an run 5 miles. I m not sure this is related in any way but I noticed 2 spontaneous bruises. A medium sized one the top left of my foot and my small one on my left bicep. Can you think of what might be causing this or refer a tye a specilaltist to see?