Some "flares" or bad gut times, can definitely last longer than we want them to. I remember very very sensitive times with my tummy lasting for weeks, especially at first. I also remember bad flares lasting sometimes only a couple of days, but returning to an uneasiness, and very restricted diet until (and I was lucky with this!) I would have a more normal phase for a little while.
Loss of appetite can happen, but to lose 14 pounds is a bit dramatic. It might help to eat fairly bland foods but calorie rich, such as plain carbs to help settle your gut (rice, peeled and mashed white potatoes, maybe pasta etc), and simple proteins like eggs, fish or lean meats. Chicken is very good rather than some more fatty meats, at first.
Adding a tiny bit of salt (if it's OK for you) to foods can stimulate the appetite slightly, and make the food more appetising.
There might be a few vegetables you can tolerate? If so, do try to include them. I find baby spinach (wilted or lightly steamed), green beans, to be OK for me, but we are all different. Some people are able to happily eat cooked carrots or other vegetables.
But I think we have to work out what is okay for us individually as we are all so different.
So if by eating some easily digested plain foods you can just get a little bit of help to settle your tummy, and get some nutrition, that might help, and you can gradually build from there? In order not to get malnutrition, a good multivitamin and mineral complex one-a-day tablet might help. But be sure that's OK for you and not against doctor's advice. If you're not sure, check if that's OK with your doctor.
I don't know if you've ever had a dog, and your dog got an upset tummy with diarrhoea, but the vet would always recommend one thing : plain boiled rice with boiled white fish or chicken, and nothing else but water until the gut settled, then gradually introduce other foods carefully. Well, that can work for people too, to get over a very bad flare up. It's actually quite good advice, for us, as well as our pets.
I am guessing you have been diagnosed with IBS? So it's not something else going on.
I hope you will start to feel a bit better soon.