I would give him a 5 day course of Panacur guard, I know you have already checked but sometimes you miss the hatching stage (that happened to me once).  You don't say what you are feeding him, but a feed which helped my horse is Allen and Page Calm and Condition, you feed it wet.  I used it with sugar beet and alfa a oil, and added in some flaked barley over the winter and my horse put on really good condition with that.  However if you're unsure you could always email one of the feed companies and their feed consultant will be able to advise you.