Left shoulder pins and needles down my arm, my index finger feels numb, feels like the blood flow is being trapped but chronic aching/hurting ?

Pinched nerve: Pins and needles from shoulder to hand can be caused by pressure on a nerve in the neck exiting the c-spine. See your doctor for evaluation .

Brachial plexitis: inflamation of your brachial plexus, group of nerves that come together as they are coming out of your cervical spine. This in my experience usually responds to a course of steroids, although for some reason the literature calls it "self limited". We usually don't know the cause, can be viral, due to a chronic inflamatory condition like lupus. Rarely due to spread of cancer. Should be checked.

Several reasons?: Could be a pinched nerve within the neck compressing C-6 nerve root, could be brachial plexitis, could represent more distal problem at elbow, such as pronator syndrome. Need to assess precise location and causes, as treatment far more successful under certainty.