What Causes Weakness In Hands Along With Weak Thumbs?

47 year old female. Non smoker, very light drinker. I exercise 3 times a week. Recently my hands have become week especially my thumbs. Almost to the point of not being able to open a bottle. Last night after hot yoga my arms and hands were so week, I was concerned about driving. Also I am very cold, I live in a cold climate, but so cold I'm concerned. Can't sleep, I'm so cold. Thoughts.... I am a special education teacher, not typing a lot, but in the past have had to restrain students, that's when I first noticed the week thumbs. But it's all the time now....