I wish I had some firsthand experience to relay with spider bites but do not. I do however have firsthand experience using poultices to heal infection of the low limbs .... you may remember my experiment gone awry painting a rash on foot suspected as eczema .
You said poultices rock but there are various to employ. Did you do cabbage, that post was around the same time you posted about " look infected?". I did well with slippery elm as the main ingredient mixed to a moist mud like glob applied generously to site of oozing body part. If you have some marshmallow root/powder to add, that should help sooth and draw out whatever is causing puss, sepsis or other decay of tissue. Also some echinacea root or plantain leaf are specifics for stings, bites, poisonous, venomous and the like. God speed.