I also don't recommend just giving antibiotics until you know what kind of bacteria you are fighting, and then dose the appropriate antibiotic to the disease.
this is why we are having disease resistant germs, but also if you have a gram positive bacteria and give a gram negative antibiotic, well you aren't doing a thing.
Plus, you need to test the snots, etc before the horse is on antibiotic.
Understand your PTSD, but proper medical protocols should be followed, not just willy nilly giving big gun antibiotics just because.
Most definitely you need to address this asap, particularly if the snots are just out of one nostril. My mare started out with very mild strangles and ended up with a gutteral pouch infection. Spent a week at the vets on IV antibiotics and having that pouch flushed out daily. Yellow snot is never good.