Although many if not all will deny this in my opinion you have parasites.
(Problem solving in abstraction is just that - an academic exercise that may in the absence of experience and education miss the mark completely.)
Antibiotics can make things much worse (as they kill off the stool producing bacteria in our bodies). Taking probiotics is becoming a common recommendation when taking antibiotics (my family's found enzymatic pearls to be an effective OTC probiotic).
How long have you been resorting to Immodium? (have there been earlier episodes?)
You appear to have been grossly mistreating your body through your eating practices. During your present distress perhaps now's a good time to take a step back and reconsider.
Sorry about your situation. I have some experience in problem solving more than anything, but key issues are gaining a TRUE diagnosis. You are NOT just human cells but a community of bacteria which you do need and which your body can cooperate with. (check how vitamin K is made in the body). The body is happy with all it's "acceptable" critters and unhappy with others. Immunity (rashes/pus/etc.) can be a NORMAL response or gone bonkers to a foreign bug, which sounds like your situation. There's a lot of immunity in the GI tract, so is it still there? hidden in the dark areas of your appendix?/elsewhere? or has the immune system just over reacted? (IgE) Persistence to knowing EVERYTHING (stress/diet/medications) is key to YOUR body. You started w the basics, but use response time as your guide to move on. I always tell what i've done ALREADY, so docs don't repeat non-working therapies. I always ask HOW LONG will this take to show that it is WORKING. Antibiotics should NOT make things worse, but hold it's own for at least a few days to improve definitely towards end of "therapeutic dosage time given". If a "general" antibiotic doesn't work then you need to have a culture test to know what's causing the issue. You should study what diseases your occupation exposes you to. It's easy to give up and let the "experts" handle everything, but learn to learn/study from this will help you in the future. Here's a recipe that doctor's use:
C/C chief complaint in patient works (subjective)
HPI: hx. of problem asked by provider (objective)
Med. Hx.: Your general med. hx.
CC: Findings of YOUR issue that provider physically checks for.
Tests: Specific tests related that needed to determine issue
IMP: Impression (LEGALLY required) which can be wrong, but
must have in order to give any therapy/med. It can change.
DISP: Disposition or 1 short term treatment plan vs
2 - long term treatment plan.
So that's one "recipe" that you can use for yourself/car repair/whatever, but
it takes study/learning. If you don't have time, then all you can do is ride
the bus and hope. Helping yourself, helps others. Good Luck.