Belle, If he is responding to you (your touch or your voice) it is probably nothing to worry about, simply an immature nervous system. I would definitely mention it to your health nurse or GP next time you see them though so that they can check him over thoroughly and put your mind at ease. If your mobile phone has a video function, maybe record him when he is doing it so that they can see exactly what you are describing (10 or 15 seconds would be enough).

He is gorgeous, by the way, congratulations!