I unfortunately/fortunately moved to an area in Texas where every allergy is a CAT IV. Love the area, and the area loves me like a movie where a writer meets his #1 fan :) ...
I can get bouts of hell down there, where it feels like Chuckie the doll is thrashing the inside with his knife.
For me what I figured out it is due to inflammation, dehydration, and a chemical imbalance like you stated. Stress effects it (remember the gut has the same chemical composition as the brain), and it is critical movement occurs to help the waste flow through.
It is rough as hell.
It hit me after I was put on some strong immunotherapy drugs due to the 24x7x365 desert climate with huge bouts of rain. When the drugs worked the likeliness that I had these systems went away. If I had an allergic reaction ... holy hell watch out cream or fish or peanuts .... it is going to feed the beast.
So the key I found is to take multi-vitamins (b like you stated), drink lots of water, walk, and keep stress levels down. If you know you have an allergy hit coming, beware and take care of what you ingest.
Which makes life a little bit harder, but it is what it is.