I mix dried Greek Oregano into my flocks feed daily it is a natural antibiotic also, and ACV with mother is really good too as was mentioned. I use it a couple times a week in my flocks water buckets.
I hope he makes it to the vet. I would check to see if you have any antibiotics or do you possibly have an Oxine ah?
https://www.backyardchickens.com/threads/oxine-seems-fabulous-users-please-share-usage-dosage-storage-etc.562407/
What have you done for him? any meds? any chance of a vet visit? Since he is sick he should be inside where he can stay warm not by a heating element but in a room that is not freezing since he may have fever. Please answer the questions. and also do you have any antibiotics human or animal...