I am not overly familiar with IBS- but the symptoms sound like it could be IBS. Are the doctors not taking you seriously due to your age or something else? When I was 20 I had gallbladder issues, but they wouldn't begin to even look at that because I was so young and the didn't think it was possible- but sure enough- a year later, I finally was able to get some help. Keep pushing the doctor for answers, sometimes they brush off patients too easily due to them not fitting in the 'box' of who should experience what.