Constipation, good times. I always get constipated when I am out of my normal environment. And one time when I went to Europe for 2 weeks, I was constipated the entire trip! I was so uncomfortable by the end. Abdominal pain is part of constipation and weird stools after as well. Improving what you eat should help. Here is what an ER doctor told me to do with my son for severe constipation--- grape juice. Simple grape juice. A full cup every day. Also eating fresh fruit helps such as strawberries, etc. Working on your fiber will help too. I do get very pale stools when I've had a high level of dairy. And stool color changes are common when constipated. However, you need to have this examined so I'm glad you are going to a doctor. Bile could be lacking (which is what gives stool it's lovely brown color). Why is it lacking? That's the question. Things that cause it are a blockage, cyst, gallstones, etc. All those could also cause the pain you say you are having. So, if you are eating foods you don't usually eat or a lot of dairy, then the stool color wouldn't matter and should go back to normal in a few days. But otherwise, you should talk to your doctor (as you are) about this.
So, let us know how the doctor's appointment goes. Would be great if you could see them sooner but then again, you will know when you see the doctor if your stool color issue resolves. good luck and stay in touch.