Are you urinating more than usual. If so see a urologist it could be Interstitial cystitis.
Does the pulsation go with the heart beat?
I was sure it was an duodenal ulcer: pain on empty stomach releaved after eating is a typical sign. It is really interesting that Kefir helped you (maybe it was a coincidence...), maybe kefir built a thin lining over an ulcer and protect it from the acid. You might want to have a stool test for occult blood (Hemoccult). Duodenal ulcer may be diagnosed only with upper endoscopy though.
That pulsation was like a muscle twitch, like a spasm which repeats few times and subsides? Or was it constant and related to heart rhythm - in this case, my only thought is abdominal aorta aneurism. This should be seen on abdominal CT, but CT maybe wasn't done on the level of aneurism...Abdominal pulse may be felt in skinny persons regularly. Diagnosis is with ultrasound.
Light colored stool is from less excreted bile, which may be blocked on the level of bile ducts (usually due to gallstones). Ultrasound is not reliable for diagnosis, so HIDA scan should be done. If it is gallbladder, pain would be under the right rib cage, and would appear in minutes/few hours after eating a (fatty) meal.