Hey Euphmorning,
Same exact issues here, only mine are on the right side, and I have an ever so slight numbness at the tip of my right index finger. I experienced a terrible pain in my upper neck on the right side after playing basketball one night 5 months ago, and the pain was so bad that I could hardly turn my head to the right. The pain subsided over the course of a week or so, but it was replaced with insane weakness in my right arm; I couldn't even get a ball into a basketball hoop from 3 feet out. Shortly thereafter, I noticed significant atrophy in my right triceps and chest.
My strength has since recovered to the point where I can shoot 3 pointers, but both my chest and triceps are still small and flaccid. I also get constant twitching/fasciculations in my triceps, chest and lats. I had an MRI done, and that showed bulging discs at C5-C6 and C7-C8, with mild to severe foraminal narrowing in both. My neurosurgeon still remains perplexed, however, citing that those nerve roots and their associated branches don't innervate the pectoral muscles. The brachial plexus is a fairly complex nerve system though, and based on my own research, there appear to be branches that do in fact innervate the pectoral muscles.
Have you looked into Brachial Neuritis (also goes by Parsonage-Turner Syndrome and Neuralgic Amyotrophy)? Several folks on this forum mentioned having the same exact issues we're both having, and were diagnosed with this disorder. Thankfully, it sounds like recovery is highly likely if this is in fact what we're suffering from. Curious to hear others who've had similar symptoms.