Is this giardiasis

A little list of symptoms for you.

Belching with a "rotten egg" odour; Foul-smelling flatus; diarrhea that starts as mild and becomes watery.

These symptoms occur in that order over the course of 24-36 hours. They then abate for 7-10 days and repeat. For the last six months.

Several courses of metronidazole have had no effect. A stool sample showed negative for giardia.

So... do the symptoms fit or might it be something else? If somethiing else, what? Tearing my hair out here 'cos it's damned unpleasant to have.

Simon.