What the heck is wrong with me?

I think my issue is malabsorption.  I take a big multiple vitamin pack each morning.  Has lots of B vitamins.  When I was healthy, I would get intensely yellow neonish urine within 2-3 hours.  Since I have been sick (almost 10 months now), the worse my symptoms, the more clear (to completely clear) my urine.  If it does get fairly yellow, it takes 8-10 hours now.

Have symptoms of diarrhea (haven't had a normal fully formed solid sample since this all started), general fatigue, no appetite (though I force myself to eat), lost 45 pounds, sometimes shakiness and faster heart rate.  And the severity of all of them move together.

Eating a lot of sugar makes my symptoms spike badly for at least 2-3 days.  Been eating a diet with a bare minimum of simple carbohydrates for a week now.  Mostly meats and vegetables.  Haven't gotten a whole lot better, but not worse either.

Had a colonoscopy and endoscopy.  Neither found anything interesting.  Had lactolose breath test, which only spiked a little bit.  Went from baseline of 2 to 15, not the 20+ usually expected for a small intestine bacterial overgrowth.  But I did just see an article in the American Journal of GI about a study with people having IBS.  Most of them got better with antibiotic treatment, but only like 10% tested positive on the breath test.  Is this test really reliable?  Also tested for Celiac's disease - negative.

This all started when I had a cavity fixed, but the tooth died, massive pain, ended in root canal.  But I was taking like 3 grams of ibuprophen a day for 4 weeks.  And lots of antibiotics too.  Figured I might have messed up my healthy flora pretty bad.  And maybe even that muscle sweeping action of the small intestine.  I have read that can happen too.

I would greatly appreciate any insight, knowledge, or experience anyone has.  This issue has trashed my life for 10 months now.  Thanks.