Oh I just posted & lost the post.
Thank you so much. Sorry for the wobble, just suddenly felt really awful. This week he has been so brilliant, smiling, alert, sleeping better and grasping his toys, I had almost forgotten he was 'failing to thrive'...
You have all been so lovely and I feel a bit more rational now. He is wearing a nice stripey newborn babygro my sister bought him so she is pleased and he's being passed round admiring grandparents.