Those head lesions look like Avian Pox or Fowl Pox. His other symptoms might be a secondary infection. A quick Google will give plenty of info on it.
Threehorses gives excellent guidance; I would do as she said.
https://www.backyardchickens.com/forum/viewtopic.php?id=3569
In addition, feed, treats, and whether he free has access to a yard, woods, etc. would be helpful.