College is much different from high school, even if the material seem similar. The classes are larger/smaller, the "working together" less (which made a difference to me; there's a togetherness about learning in high school that goes away with college/being an adult with everyone doing their own thing).

I would simply back off on how many courses you attempt per semester until you find how comfortable you are with each "kind" and I wouldn't take so many math/science ones at a time (unless you were planning to "major" in a math/science curriculum). I know when I went away to college I got straight C's the first semester and my stepmother commented on how one couldn't figure out what I was good at or bad at :-)

But I found the second time I went to college as an adult, just taking 2-3 courses a semester (and 1-2 in the summer) worked extremely well, especially after I figured out how college worked and how to get good grades in college, what professors seemed to want versus high school teachers. I would find the support center at your school, see about study skills or tutoring help, etc. and see if you can figure out exactly where you are having your difficulties and if you can work them out. I'm pretty sure taking a course a second time "cancels out" previous bad grades (instead of averaging them like in high school) so it is truly just a learning situation to find out how to master that particular class that you have to go through.