Yellow stools, other symptoms for over 2 months

Hi all,
During last Chritmas (i.e. over 2 months ago) I had  a mild food poisoning after eating in an Indian restaurant... or at least I thought so...there is no way I could know for sure. I had some mild fever and stomach cramps lasting for a day or two. The main concern of mine was the stool color. It became yellow which lats to this day. It actually comes to darker or even normal color if I avoid fatty foods and alcohol (all I drink is beer anyway... i.e. used to drink). However my stomach became somewhat sensitive to fatty food (especially things like cheese, mayonnaise, etc. i.e. all the "really bad" stuff). I don't feel pain in the stomach but just some bloatin and as if I had eaten something really big and nasty in the upper part i.e. where the stomach or pancreatic and gallbladder symptoms would normally occur. Of course, I did lots of reading and realized it may have to do with gallbladder, liver or pancreas. I also went to my GP (three times by now) who sent me for a blood test (liver and kidneys) and abdominal ultrasound can. Both showed absolutely nothing even though the symptoms continue. In the end all my doctor told me was to avoid fatty food and said it may be stomach acid because there are no indications of anything serious. He suggested to try some antacid medication which i may give a go.

Of course, I understand that eating habits (and mine are quite horrible without any exaggeration) may have to do with such disorders, especially once eating healthy food I see an improvement. However I am concerned why it happened suddenly? I am in my mid 20's, so it shouldn't be something that "comes with age" and have never had any stomach disorders since the age of 4 when I had gastritis. Ever since, however, I could eat stones and rocks and it wouldn't make me feel bad. I just wonder if there is anything else I should look for which could have been missed by a blood test and ultrasound or should I just change my eating habits? I know that various types of stomach cancers may cause such symptoms which made me particularly scared.