what is the course of sulfur burps + diarrhea outbreaks?

Hi, I am Elisabeth, 24 years old, from Denmark:
I have had sulfur burps, diarrhea, and vomitting 3 times within the last year, lasting each time for about 3 days.
First I wasn't too concerned myself, but now I have had exactly the same at least 3 times, and the sulfur burps were very unpleasent and seems to me to be a very particular and unusual symptom.
On this site I can see that other people have the same symptoms as I occasionally have, and sugestions like giardiasis have come up. I have seen my doctor and have sent in 3 samples with stools, but they have all been negative. Since I was very upset about my condition my doctor sent me to a specialist who made a biopsi of some tissue in my duodenum. This sample showed nothing.
Since I thought I had giardiasis I have stopped eating meat, and I eat garlic pills to purge the parasites, if I have them.
Is it possible that I actually do have the giardiasis even though the samples didn´t show anything?
How can I establish the course of my "outbreaks"/illness?
I haven't experienced weightloss, but I do have headaches allmost every week and I think there could be a connection?
I have 2 small children, so my doctor thinks it is just a virus or something that I get from them, since they are in day care (that's normal in Denmark), but they don't get the outbreaks.
My husband has had one "outbreak" allmost the sime time I had my last one. Did I infect him with something?
I think the outbreaks will return, so I am very interested in finding the course. I also feel very bad if I infect other people without knowing it.

I hope to hear from someone with a solution
Best regards
Elisabeth Andersen