Don't give up! I'm starting my senior year of high school next week (woohoo!) and I remember what it was like freshman year. I was super stressed about all of my grades, even if it was something simple like gym class. Remember that core classes count the most when colleges look at your application. They also want to see that you've taken difficult classes throughout high school. Since your GPA is higher than a 4.0, I assume that you've taken some Honors/AP/IB classes. This is good! Colleges like to see that you challenge yourself. Getting a B in an Honors/AP/IB class is worth more than getting an A in a normal class.
Maybe it has just taken you awhile to adjust to high school classes and homework? It's important to get down a solid routine and habit of studying, reviewing, and taking notes. These skills will be essential Junior year, which is when most students take their hardest set of classes (since colleges will be focused on junior year, since fresh & soph years are often focused on requirements like gym and electives). I would really try focusing on getting down a study routine, as (I assume, but I've never been there!) it would be VERY important to have when it comes to studying for the MCAT and getting into med school.
If you really feel stuck and you can't pull anything higher than C's or B-'s, then I would consider dropping one or two of your classes to an easier level. This will give you more time to study for your other classes and learn the material.
Above all, remember that high school is supposed to be fun. I've also read that you shouldn't worry too much about how you do in high school; college matters most (kind of like how the ACT/SAT doesn't predict college success). I think one of the biggest mistakes I made as an underclassmen was working hard and studying when I just didn't have to. It's not all about the grades! Extracurriculars, having a job, and other commitments are important too and colleges will also be looking at that.
Sorry, this is kind of a meandering answer, but I hope you found some advice and comfort in it.