I think any science major is inevitably going to have that one semester where they have to load up on sciences. I had cell/developmental bio, biochem, pchem I, differential equations, sociology and research fall of my junior year... that entire semester is still somewhat of a haze to me right now. It was doable and it didn't tank my GPA (though it was the lowest that I had in college by a big margin), but I definitely had to learn how to work the system, knowing when to attend class, when it was ok to skip class to catch up on sleep, and how to study smarter rather than harder (there just weren't enough hours in the day). I couldn't have handled it my freshman year (even though I was much more gung-ho and motivated freshman year). For some majors, it's unavoidable. You have pre-reqs that have to be taken at some semester or that is only offered during one semester, you have research credits that need to be taken, you have that one class that you told yourself you were going to take and it's only offered every 2 years, etc. etc. and it all adds up.