Your post remind me about what happen to me when i go to juice fasting, i started to get gut pains more after one week,and it just get worse day by day, the i realized by reading about copper toxity that the diet itself just juices was making copper toxity worse and i stopped the fasting , had to of course do it slow but after few days when i was back to eating meat and taking zink supplements the pain started to go away. I dont know could this be also your issue, but take it as one theory and maybe test by taking good zink supplement .
I hope there will be a solution for you, pains in gut are so horrible .