My daughter started having symptoms of IBS at around age fifteen. Same symptoms... even the ones you don't care to mention! It's easy to tend, just gotta get enough of both kinds of fiber and not overeat. She had an anti-spasmodic and an anti-depressant for it but lost her insurance so her symptoms came back. It's no fun at all.
Nothing at all like that ..maybe worms or "amaebiosis " for which medicine is required.
Try taking some probiotics, like activia yogurt...or they have probiotic tablets. Sometimes we get something called a yeast overgrowth...that means that you had a little too much sugar or starchy food in your diet, and maybe not enough fiber, and this yeast starts building up and growing too much in there. Taking probiotics will start good bacteria growing inside you, and they will help to control the yeast. Eating more food with fiber, like beans, celery, oranges, etc, will also help to clear things out.
Have you taken antibiotics for anything in the past six months or so?