I'm 16, I also suffer from IBS and foul smell. My social life has been destroyed by this all I have to focus on are my grades. I have been going to a gastrologist and have had to change my diet and take lots of supplements but I have made no progress with the odor. It keeps me from reaching my fullest and kills my confidence.
Also be aware that some people have cryptic tonsils. The stones can be cleared out various ways if you have them. Google tonsil stones, cryptic tonsils.
In addition to what has already been said, because it all goes along with what I'm about to suggest, check out this site about food sensitivities. It is very good. It definitely talks about gluten intolerance and really much of what I've been talking about myself for a few years now:
http://www.whfoods.com/genpage.php?tname=faq&dbid=30#what
Check out what they say about avoidance diet and elimination diet, too. It goes right along with the GI territory and the migraine territory. I actually found this when I researched what someone else posted about Tyramine Intolerance and migraines. For me, it hit the nail on the head as I read this web site. I already know I'm sensitive to all those things that it talks about.
I did notice that eggs weren't mentioned with the sulfur foods. They should've been. Carrots and Cherries are not hypoallergenic. Neither are apples. I know lots of people who have problems with these foods. What they said about spinach is right on. Lettuce has to be included for me, as they are close cousins. I know of several people with similar issues who also can't eat lettuce and spinach, so I know that what I'm saying is accurate. Grapes, garlic, onions, cabbage, and gingerroot need to be included in the sulfur group. I noticed some of those were missing. Not all things are going to be equally a food sensitivity for all people with these problems, but there is a pattern of things that are pretty consistent for a great majority of us.
Still, overall, this web site is quite accurate. And, yes, these sensitivities can cause dental problems. That is also on this website.
There is help. My husband suffers from alot of sinus drainage that contributes to his breathe. But most of the time it comes from the stomach. Have you spoken with an ear nose and throat doc? or a dentist? Let me know and I will ask mine if you haven't.
Try a gluten free diet and see if it helps all of the above.