Post-nasal drip can be a sign of histamine response. Stopping the drip itself is probably not as important as stopping the cause. (It seems likely you're aware of this, since this is one of the defining criticisms of conventional medicine.) Look for other signs of histamine release like hives or itching (like itchy ears?).
Histamine response can be from dehydration. One possibility. Clearing vitamins and drugs is helped by proper hydration. Try drinking 6 oz. of water every hour, even if you pee it right out. Work up to it if this isn't your current level. Look up "oral rehydration therapy" to figure out how to better hydrate yourself.
Note that if you have adrenal issues and thus low aldosterone you may be losing more sodium than potassium, so you would probably want to add salt to your water/food.
Histamine response may also be from food sensitivities or intestinal issues. Stress makes your gut more permeable, which can lead to a lot of problems. Take note of when your runny nose happens -- is it worse after eating? (You could also be experiencing a kind of dehydration during digestion.)
Reduce your stress as much as you can. Not just your stressors, the things that cause you stress, but your reaction to them and your subsequent stressed-out state. Eliminating stressors can be hard. Changing your response to stressors isn't easy. But adjusting your general state of anxiety is something a little easier.
Practice breathing exercises, like what Dr. Lam suggests.
Try meditating. If it's hard, try assisted meditating. Here's a sound file. Listen to it with headphones on.
. It's a complete half-hour meditation using "binaural beats". Whatever method you choose, don't give up if you fail to get into any obvious relaxed state the first few times. When trying to relax try counting breaths, or gently and slowly swaying forward and back, or stretching your muscles beforehand or doing yoga.
Try listening to relaxing music, really listening to it -- paying attention to all the tones and melodies and rhythms and try to focus on the music, gently bringing your focus back when you notice it wandering.
Try playing a musical instrument if you know how. Or do anything that's attentionally immersive (but that isn't also stressful -- like first-person shooter video games).
I imagine your body is in a catabolic state. That's what I've previously thought was related to my similar breathing issues. This coincides with your weight loss. You might test your ketone levels with ketone test strips bought at a local pharmacy. The breathing could be a mild form of "kussmaul breathing". If you read up on it, don't focus on the more extreme form and the worries related to it. Note that _I_ had labored breathing, feeling like I wasn't getting enough oxygen, but have improved since. I must confess, though, feeling short of breath _sucks desperately_. But there's hope.
Improve your body's nutrient absorption. It's absorbing at some level right now, and you're surviving, but the better your absorption gets, the better you'll get. Relaxation techniques will help your gut not be so permeable. I guess glutamine is also good for that. I think zinc may also be important.
High fiber foods can be counterproductive for intestinal problems. I'm only just exploring this part of my health problem, so I don't really have advice here yet. Maybe read "Restoring Your Digestive Health".
Keep a food and symptom diary.
I would expect the digestive enzymes and probiotics to be doing you a world of good. Maybe try testing larger doses of the digestive enzymes with your meals.
I don't know if I should mention this because it seems counterproductive if your body's already catabolic and you've got adrenal issues, but fasting made me feel better. I don't recommend it as therapy, but perhaps as a diagnostic procedure. Maybe dangerous in your state, though. The two things I think fasting did were a) gave my gastrointestinal tract (GIT) a rest and b) forced my adrenals to release cortisol to raise my blood sugar. The combination of these two probably made me feel better. Maybe a low-fiber juice fast could work better.