First, a little background: my gastroenterologist diagnosed me with IBS when I was about 16-17 (I'm 21 now), although he didn't do any particular tests. I used to have stomach aches, gas, bloating, and almost exclusively constipation. Every once in a while, I do get diarrhea, but that's pretty rare.
Now, I don't usually get that many stomach aches, but I still have the bloating and sometimes gas (depending on what I eat).