Why or why

I suffer with ibs and must be diarrohea and constipation.  I can go weeks with a regular stool movement each day although can vary in consistency and then 15 mins after eating one day can have diarrohea and then not have a movement for a few days.  This then lead me feeling exhausted and a tender belly next day.  Why does this happen and does anybody else feel like this.

Thanks.