I don't have a science/math GPA to write home about. This is due to a combination of reasons:
1) 5-unit science courses are a lot harder than high school science courses. 😀 I just wasn't prepared for the amount of material and the difficulty of the material. Unfortunately, this took me 1-2 semesters to understand before I finally "matured" and understood how to successfully pass a tough course with a good grade.
2) I worked full time my first 2-3 years of college because I was responsible for a lot of my own expenses. This hurt in the time management department. When you go to school from 8am-12pm and then work from 1pm-10pm, it's hard to find time to study. I found a better job that pays better, so I don't work quite as much now. Just dropping 20 hours a week of work has made a huge difference in my grades. If you're lucky enough to not have to work full time, don't!
3) I didn't know exactly what I wanted to do. This is a horrible excuse, but I did not give 100% effort my first year or two of school. If I knew I wanted to become a pharmacist, I know I would have worked harder earlier on in my education. Again, this is a stupid excuse, but it's pretty common to see.
Now that I've "matured" as a student and I'm working less hours, I'm getting better grades in more difficult courses. For example, I received a 3.0 my sophomore year only taking 15 units of intro science courses and lower division GE. Last semester, I received a 3.8 taking 20 units of mostly upper division science courses.