Very nice portrait!
A quick critique to help you improve:
the arm and hand are too thin and small and the pose does not visually connect the arm to the rest of the body. it almost looks as if the hand belongs to someone else reaching up from below. If you look at most Portraits you will see that the hand is much more "on " the face instead of "under" it to prevent it from looking like uncomfortable. Here are a few examples:
Notice how long the hand is in the last two pictures the fingertips almost reach the eyebrows.
Hope this is helpful to you. Keep drawing and improving !