HELP! My husband is very ill

This may be long so I thank you in advance for reading. My husband 41 has had stomach issues all his life. About 8 years ago they escalated. Watery stool every time, weakness, throwing up, joints hurting, loss of muscle mass. We did all the doctors and all the tests. EVERYTHING came back negative. It was very discouraging. Finally it was suggested he quit gluten. We did that about 5 years ago. Things improved. Took about 1 year for the stool to improve. He has not been able to gain weight AT ALL and actually will lose a number of pounds by sweating or any kind of physical labor. Lately it has gotten worse again. He is still gluten free. Now we are back to complete fatigue, watery stool all the time, throwing up. This is not every day. But when it does happen he is down for about 3-4 days and will lose about 4-8 pounds. His muscle mass is deteriorating. I've been doing research and think maybe it might be Small Intestinal bacterial overgrowth SIBO. Is anyone familiar with this? Has anyone had these symptoms?  Or are there other bacterial infections that might cause these symptoms when left untreated for a long period?

​Right now the doctors just want him to restart all the same tests that came back negative in the first place. We feel this is not a great approach. Please any give me some suggestions of what might be happening. What kind of doctor can he see that will think outside the box and the normal tests?  Thanks for reading this. 

Hi mind65094

Can you be specific when you say 'any kind of physical labour?'

Sorry for that its Gastritis,avoid acidic food/fruits and he should eat many times in a day

Hi Mary. Physical labor would consist of working the yard (pulling weeds, shoveling, chopping wood). Also he was working cleaning carpets and when it is hot outside and he sweats a lot he can become weak, light headed and nauseous. He has zero appetite most of the time. 

Thank you for your comment. This was ruled out by the doctors. At this time he doesn't eat fruit or anything acidic. Mostly just protein. 

Hi mind 65094

A lot of physical exertion can impact on the adrenals and release high levels of cortisol from the adrenals and this can cause gastro problems. Perhaps have his cortisol levels checked also his vitamins and minerals. Vit D levels can cause gastro problems and painful joints along with B12 deficiency which can cause weakness and fatigue..has he had a full blood count including vits and minerals also a Serum B12 blood tests..they are worth testing just incase, and they can easily be put right...

Hi mind 65094

Sorry! Intended to write 'LOW' levels of Vit D can cause gastro problems....

A gsstroenterologist would help.  Having the tests repeated may be useful to see if anything has been missed the first time round.