Squibby - I think course loads also depend on the school you go to. The undergrad school I went to is known to be one of the most academically rigorous schools in the country (at least according to Princeton Review). So 4 courses was a normal load (and advisors generally suggest that freshman take 3 courses their first semester). You had to petition to overload if you wanted to take 5 courses, and the few students I knew who did overload ended up hating themselves by the end of the semester. However, I know that at the majority of other schools, 5 courses is a normal semester load, which I think is because the work load per class is less, and therefore 5 classes is more manageable.
In general, I think it's sometimes problematic to compare yourself to other folks on here when they go to different schools, and that a better way to figure out if you're taking a heavy enough load is to compare yourself to other pre-vet/pre-med students at your school.