I have prominently IBS D+ and I always find that it is exacerbated by stress/anxiety so that could well be the cause. However I often find that it is a number of things that trigger mine and sometimes I don't even know why, I just get an attack seemingly out of nowhere.
As for cramps and pain, unfortunately I'd say that's pretty standard of IBS, when it's flared up. I rely heavily on Colpermin (peppermint oil capsules) to help with these symptoms and they're pretty effective most of the time. Other people have had success with Buscopan tablets or Mebeverine (unsure of trade name, Colofac I think?) so you could try either of those. But I don't believe you can interchange any of the above or use in conjuction with each other.
I think there is a helpful post at the top of this topic section, going into detail how IBS works and the symptoms.
It's unfortunately quite common and, I find it difficult to talk to friends/collegues about it as the nature of the problem is quite embarrassing! But I find this forum helpful as it makes me feel less lonely or down about it.