Coming out of lurkage because my experience was so similar. In my case those same symptoms were indicative of ulcers, leaky gut, and general bacterial problems in my gut. There is already lots of good advice here. I wonder if you have celiac disease because your symptoms fit perfectly.
I personally got rid of 95% of problems by eating 0 carbs for as long as I could, which was a week. That will starve out any bacterial overgrowth. I did consume lemon juice as a digestive aid and I think it is a much better one than ACV.
Then you need to make your good bacteria happy and your gut wall into a fortress. That means not torturing the poor bacteria and muscosal layer with fiber and antinutrients. Yes, that means no prunes, dried fruit, grains, and other outdated gut torture devices. They work on a technical level, but like enemas, they do not address the real problem and the BMs you get come at a real cost for the gut. You may feel bad without them at first, but eventually the gut should sort itself out again.
Grains, legumes, caffeine, and nightshades can also contribute to leaky gut.
I have consumed fermented foods/probiotics too, but I don't think they are very effective. The bacteria in them do not colonize your gut, so they are not a real solution. A real solution works with your own gut species mix to make them a happy balanced ecosystem. Maybe try them simply to phase out the fiber stuff?
If a meat is unappetizing, like the ground beef, you should probably considering ditching it in favor of something easier to eat raw like fish. Fish is also great because it can help you correct the poor omega-3:omega-6 balance so many people suffer from. Omega-3 fatty acids are important to the function of the gut's "brain" and to reducing inflammation. When you eat too much omega-6, your body cannot use the omega-3 as efficiently. It's way I no longer eat almonds or avocados....they are omega-6 bombs! I track my omega-3:omega-6 ratio very carefully because it is so important for brain, skin, and gut. Usually my ratio is 1:1 to 1:4.
Once you want to move back to including some carbs, I think smoothies with greens and berries are the way to go. You should strain them out to get rid of gut-irritating seeds. These should also help you gain some weight.
I've fixed myself this way twice now
I got myself into such good shape that I thought I was invincible last year and I admittedly partied, ate cake, and took ibuprofen enough that my symptoms came back. It's annoying to do it again, but it taught me a valuable lesson about not taking a good thing for granted.
I am working with honey bees now and I hate to admit it...but honey, even raw fresh honey, is candy. I was eating it all the time recently while working with hives and it was making me feel crappy.
I use coconut oil, but it's also a treat.