Welcome to HealingWell!
Has your doc done any tests to rule out anything other than IBS? I must say, however, you sound like many of us. Social situations seem to come with a lot of nerves, which causes D for many of us. I actually have IBS-A (alternating between D & C) so 1 second I can't go and then the next the flood gates have
opened. I'm in my late twenties, but this all started in my late teens... It was a tough battle to deal with during school, I understand.
YES, I have tried Yakult! I'm shocked someone else has tried it, let alone seen it.
Did you find it in Brazil? I am originally from Brazil so I grew up on Yakult (kids love the stuff!). You know, you CAN find it in the US (I'm in CA). I find it at Brazilian stores and even asian markets. Many of those large asian markets (Ranch 99, Lion, etc.) usually carry Yakult or some generic version of it in the refrigerator or frozen food section. For probiotics you can also try Dannon Activia yogurt or simply probiotic supplements. The supplements have billions of live cultures which may be more productive than yogurt or Yakult alone. I do both... I take supplements and eat the yogurt. If you keep up the regimen it WILL help with the gas.
Have you also tried Beano before your meals? That should also help reduce the gas production.
Fiber will eventually help too... The key is to finding a fiber supplement your body agrees with. In the beginning, fiber (and probiotics) will cause you excess gas. You body just needs time to adjust to it.
I don't doubt that the extra veggies you are adding is causing extra gas. Most veggies will do that to any person. Sometimes it might just be better to reduce your intake of those veggies. You might also want to try cooking them thoroughly; eating them raw is a definite way to cause major gas.
You might want to consider keeping a food diary, it will help you pinpoint exactly what foods give you the most trouble. Write exactly what you ate, how much you ate, what time you ate it, and how it made you feel afterwards.
Again, welcome to the forum!