You could still be having gall bladder problems, even if you don't meet all the criteria; some people never even know their gall bladders are full of stones until a doctor finds them by accident while doing some other test. The burning stool (when you say "light", do you mean yellowish or greenish in color?) is a pretty good sign that you have a bile problem, as bile is an acid and when you have too much in your stools, it will burn you a new one. about the only other thing that can cause a burning in the rectum is a fissure, which is a tear in the skin around the anus, or a hemmroid. If you only notice the burning sometimes, but not with every movement, then it's highly unlikely that it's caused by either a fissure or a hemmroid. However, you can have too much bile all the time, so even if every stool burns, it might not necessarily be a hemmroid or fissure.
That being said, some people have excess bile problems without having a bad gall bladder. Something happens and their intestines either start rushing food through their digestive tracts too fast, or the intestines just aren't absorbing correctly. Either way, you can end up with too much bile left in your stool. Your other symptoms could be either IBS or gall bladder; they're not clearly one or the other.
When you go to the GI, you should expect (demand) that he gives you a hidascan for the gall bladder (may also do an ultrasound, but don't let him get away with doing an ultrasound only; the ultrasound just looks at the gall bladder, but the hidascan examines its actual function). He should also request a stool sample, which will determine if you do indeed have too much bile in your stool (make sure you ask him to check for that). He may also want to examine you to see if you have a fissure or hemmroid. Most GIs want colonoscopies done too, but I would not schedule that until after my hidascan had come back clear. If you do indeed have a bad gall bladder, then the colonoscopy is pointless. And if you do ahve too much bile in your stool, you may want to try medicine before having a colonoscopy to see if that fixes you up. Colonoscopies are for discovering severe problems, like colon irritation, polyps and/or ulcers; if take a medicine for bile fixes all your problems, then you don't have irritation or ulcers or serious polyps; those things aren't fixed by medicine (at least not very well).
What sorts of medicines was your GI wanting to put you on? I can only think of a med for bile, and/or spasmodics for pain and diarrhea.