I use to go by Toni when I was in college and some members of my husband's family still call me by that name.
I've had a LOT of G-I trouble over the years. I had my gallbladder out 14 years ago and back then I use to complain to my doctor that my stools were very pale, soft, sometimes thin, pretty much everything you've mentioned. They were always at their palest when I was living on rice, toast, bananas and Gaviscon.

In addition to these symptoms I did have gallbaldder attacks that were at first far and few between and eventually became so bad that all I could eat was cream of rice cereal and banana, but only in the morning. If I ate anything solid after 4:00 I was guaranteed a nasty attack.
I was 28 at the time and weighed 97 pounds (5'2"). I had lost 12 pounds in 2 weeks. It wasn't much fun. Even after I had the gallbladder taken out I still suffered with G-I troubles. Since they couldn't find anything else wrong with me they concluded it was IBS.
Basically IBS is a motility problem whose most common symptoms is alternating diarehha and constipation but it can also effect the stomach, esophagus and cause a myriad of complaints. There are all sorts of treatments for it from drugs that try to normalize the motility of the colon to stress management and hypnosis.
Thankfully mine has never been that bad and it only flares up in the most stressful situations.
Gilbert's Syndrome sounds like a reasonable diagnosis except you say that it's the bilirubin that's found in blood that will be elevated and not the type found in urine. Were you ever given a blood test for the bilirubin levels? Did you question your doctor about his diagnosis considering where the bilirubin was found?
Usually tests for the gallbladder are not done unless someone is complaining of symptoms. The first test they did on me was a gallbladder ultrasound after I presented to my local ER with excrutiating pain (crampy spastic pain in my upper right quadrant). It lasted 12 hours that time.
Since you seem to be in good health and this problem with the light colored stools has been an on and off thing for several years it's unlikely anything very serious. Now if you're still experiencing pain in your back or develop other symptoms/pains, unexplained fever, etc. then you'll want to consider getting another work up done by a doctor and don't let it go too long.
I know it must be hard to deal with health issues when you don't have insurance. A friend of mine had the same problems. Even after he was in a car accident he didn't want to go get checked out because he knew how much it would end up costing. I made him go.
You're lucky that you are SO young. Unless you've engaged in risky behaviour your risk of having something seriously wrong with your liver at 21 is unlikely.
Antoinette