If the OP is a STEM major then I can’t see why you guys are advising against taking two science courses and calculus in the same semester since it is not uncommon for Pre-med or STEM majors to do so because it will only get more demanding from this point on.
I don’t want to discourage the OP because I’m a student who has struggled in college since I started and am interested in STEM myself. I’m taking two math classes along with microeconomics this semester which is a tough schedule and maybe once this semester is over I can do better in the future since I will have adjusted to a demanding schedule.