kids grow slow in winter? I am worried

My son is 5 year old, he had a doctor appointmenter two days ago.

He seems only grow 0.5 inches during the past 4 months. He gained some weight though.

Should I be concerned? He didn't get sick in the past a few months and eat and play well. He had enough exercise and we took him to swim whenever we can and he is also taking skating class...

He also drinks a lot of milk already.

I am worried....