Hiya,
They generally only need worming every 6 months - so I wouldn't worry about doing that again just yet.
The coughing is most likely down to dust in the straw, they do like to bury right down into it. I wouldn't worry overly much, providing he's eating and drinking, seems bright and alert and his eyes and nose are clear. Just keep a wee eye on him for any changes.
HTH
Karen x