Well I could only guess and even if I guessed right and gave your condition a label, I'm pretty sure any more drugs or supps will just be bandaids for you or might make you worse as some have. This is why I suggest looking into a dietary change to cleanse you and try to get to the root of it.
For the sake of your symptoms, does your burning sensation feel like coming more from your nerves or your muscles? Any of your doctors suggest or rule out fibromyalgia/ME? Were you also experiencing lots of stress or anxiety before this all happened? Where you allergic to anything as a kid besides Antibiotics ?
Don't know why lying down makes it feel worse. I do see a lot of people complaining about pain worse from lying down and feelings of overwhelming anxiety when waking. I know a lot of people with acid and other digestive problems feel worse after lying down.
Does the diarrhea feel like the kind from having an infection and a temperature, or like from drinking too much apple juice with food? Sounds like the diarrhea is your body's attempt to get something out of your body it doesn't like.