Trying to figure out what's wrong with my horse..?

I have a 10 year old thoroughbred gelding... He is healthy in ways .. His feet got done last week.. He's slicked out with a nice shine to his coat.. But he has been skinny for the past three months... He looks terrible.. I believe he had worms but we have wormed him 3 times in the past two and a half months with 10cc liquid ivmetrin ... He looks better than he did and he was improving but now he's stopped and in my opinion he's gotten a little more ribby. He's on rice bran and strategy mix three scoops twice a day. We have tried so many things... We are thinking it may partially be his teeth .. He's having them floated tomorrow morning.. Someone mentioned he could have hardware in him... How would that be cured? I notice he always seems to be standing in the shade of the barn in this heat instead of out grazing with the herd... I noticed he's a bit stand-offish lately instead of trotting up to me... I have not been riding him due to his weight issue.. I do still work with him daily on the ground though... Hes my first horse so he means a lot to me... I really hate to see him like this. He was healthy but then just went downhill... Any ideas on what could possibly be wrong with him?... Or feed suggestions? I'm gonna have the vet look at him tomorrow but... Thought I'd get others opinions as well.