I had that problem too- in my case, all of the lab classes I took were weighted at 4.5 hours instead of 3.3 like all other classes. Because my college doesn't discriminate between the two, a B in a bio class is the same as a B in a music class. However, I typically do worse in science classes; since LSAC weights them more, my GPA went down. I'm not sure if that's what happened in your case or not!