What can I use if I suspect irritable bowel syndrome?

Hi, I suspect at home a team of drazliwego intestine what can I buy in the pharmacy to help myself? This bothers me very much at work very often kneels me in the left lower abdomen diarrhea and constipation alternately burrowing in the abdomen the most painful is the klujacy pain only under the left subsea. I only feel relief after putting on the stool. Sometimes I walk i walk suddenly from thenadzka there is a very strong pain such systolic as with the body. Sometimes I can go to the toilet 3 to 5 times a day. I was on gadtroscopy all showed okey I was on the ultrasound of the abdominal cavity and also showed that it is okey only I have a very large amount of gas in the gut. Help