Needing Answers?

Heres my problem, and then again my Horses problem..I have two horses, pasture horses, grain fed, with oats, safe and sound coastal hay, and alfalfa too..All shots updated...Negative strangles. In october it all began..We live in east Texas...Both horses began with runny noses, back in Nov...Was seen by vet a couple of times...One has swollen lympnodes under jaw line, and muzzle is swollen...Put on pennicillian, zmt, atihistimines, and tucoprim....Got better, then comes back...Horses was hospitalized for 3 days, had an endiscope...Treachea swollen...Everything is negative...Had blood work done and nothing has showed. We are baffeld on this whole thing..its a not snake bite, or insect bites either..Im thinking allergies, but never has had this problem before..We are in a drought, and maybe its the dust....We are taking away something different for awhile and see if it is that. His muzzle is a little swollen this morning, and jaw under neath is still hard, but not as hard as yesterday.