I get something similar myself but not so central or quite as low down as the belly button, closer to the right ribs and slightly off to the right of centre.
It depends upon how full the stomach is.
Sometimes a more distinct sharp feeling and other times more slight of a sensation.
I don't get much brain fog but I do support my bodies detox glutathione levels and nutrients to help with methylation. Taking amino acids which support ammonia detox might be helpful too.
Read up on Biofilms and tackling them. Have a look at an iris chart, Dr Bernard Jensen
made the best one, google images should have a copy.
Dr's can be really dumb and very rarely think outside of the box of they're knowledge. There is far more to health than what they know!
I get a similar thing from my doctor. My Dr smiles and nods and still cannot make a diagnosis. I could of spent the last 23 years in bed if I had not done everything to help myself.