Hi 👋🏾 I’m a 5’5 female who weighs 107lbs. I seem to lose weight quickly and I always think I have an underlying health issue. But my tests come back normal. Could my weight loss be due to a fast metabolism?

I went to the doctor today because I was having numbness in my left arm, it was moving on it’s own and I had no control over my nerves. Long story short the doctor told me because I’m so small my muscle strength is not as strong. He told me to do arm exercises with 10lb weights. But would also like tips on how to gain weight overall in a safe manner.