I had a chance to dowse him ** according to dowse, I see some issues with small/large intestine, mainly due to an infectious agent. This would explain his fatigue and of course his "sick" feeling and depression. Which are all symptoms of an infectious agent.
Infections of the small/large intestine could be viral, bacterial, fungus/yeast, or parasite. I show a stronger tendency towards parasites. How do you know it was "a stomach virus" (I underline virus).
**dowsing is somewhat controversial, I would note that my dowsing seems to be quite good on medical issues (I wish it was as good on lottery #'s !) But it should be construed as an adjunct to practical medical testing and treatment.