The picture posted above is one of Mareks disease from Cornell:
https://partnersah.vet.cornell.edu/content/md-005ajpg
Hopefully, it is not Mareks, but here is some info about it:
http://csu-cvmbs.colostate.edu/Documents/vdl-mareks-disease-fact-sheet.pdf...
He looks very sick. Could he have gotten into something bad to eat in the yard, or moldy feed? If not, I would wonder about Mareks. Are you able to pick him up, wrap him in a towel and try to get him to drink fluids and eat some wet feed? Here is a video of feeding:
What did you use for the bugs, and what antibiotic did you use to treat the sinus infection? It does sound like lice or mites. Pictures may help. Both are treated with permethrin spray or garden dust available from most feed stores. They should be repeated for lice at 10 days or for mites at 7...