Instead of constantly using your glutes(which is fine on 2 pins a wk) but rotating inj sites is very important! I can pin quads in a different place ed for about 4 days... Do I do this sometimes... It lessons scar tissue build up when you rotate! But I'm pinning prop ed so I have to have at least 6 sites, you don't need nearly this many... But try doing a wk in quads(and the tear drop is painful for first time users, so I'd suggest the outter quad(IT Band - 6" down from hip bone gives you an idea!
Also what comes to mind is you said he did the inj for the first 4... No probs, right? So there must be a technique issue IMO!
GL!