I'm a Biology-Chemistry double major. Did you not take chemistry in high school? If you did and you still had to study hard for Gen Chem I, you probably have a learning disability. If your high school education did not include anything related to chemistry than I can understand having to study I guess, but honestly, Gen Chem I is probably the easiest science class any science major will ever take. Gen Chem II should not be that hard either, unless you have a terrible professor (mine was the worst of any I've had). I got an A in Gen Chem I without studying really at all, and I got a B in Gen Chem II, though I didn't study that much since I was a freshman and still wasn't used to having to study for anything. I took O-chem the next year and tried to pull the same shit. Got a low C on the first test, studied hard after that and got A's on everything else, but it wasn't enough to bring me to an A in the class. Studied hard from the get go in O-chem II and got an A, though I worked hard in that class going every time, doing all study guide problems, almost all problems in the back of the chapters, etc. I like to think I'm a fairly intelligent guy, but I'm definitely not a genius or anything. If you go to class, read the book, and study, you should do alright.
Depending on the prof, O-chem can be almost no memorization or nothing but. My prof taught almost nothing but mechanism, so it was more like problem solving figuring out where to put partial charges, what was the nucleophile in your reactants and where it would attack, where electrons would go, etc. I loved it. The other prof on the other hand would just have his students memorize dozens of reactions without explaining to them what was actually happening in the reaction. I don't understand how constitutes as teaching, but whatever.
O-chem gets hyped up because of all the pre-meds who take it. My experience has been that 50-75% of pre-meds are quite stupid; they just have good work ethic and will go the extra mile for an additional point on a problem set. I enjoyed O-chem a lot, and though it did require a decent amount of work, it is by no means the most difficult class I've taken. Comparative Physiology and a Functional/Evolutionary Vertebrate Anatomy class I took were probably my two hardest. P-chem is easily the hardest Chemistry class.
Don't worry about it though. Part of the college experience is (or at least should be) learning how to learn and how to think and gaining better study habits. O-chem is a good class because it's a bit of a slap in the face for students who aren't used to studying. Any fairly intelligent person with some work ethic should be able to pull of a B.
Good luck.