I've had numbness in my left arm for a few weeks now and it's preventing me from having a good sleep. I've been recently diagnosed with no thyroid.?

Pinched nerve. Neck pain that runs down the arm with or without numbness and tingling sounds like a pinched nerve in the neck. This is usually caused by a protruding disc or bone spur touching one of your spinal nerves as it leaves your neck. This can often improve on it's own with rest and anti-inflammatories, but if your pain lasts greater than one week or gets worse see your physician.