My advice would be to not take them in the same semester. Math and science aren't my favorites either, so I did Calculus 1st semester and Physics 2nd. That way, you'll only have one real class-induced stress in your life at a time. I know you asked about math & science, but I would also avoid a bunch of heavy reading classes together.. until you get into your major and can't get around it. I think smart scheduling has a lot to do with success in college. Good luck!
