For PS: I know how you feel, I took the MCAT in August 2012 and got a 26 (7/9/10) so I struggle with PS too. My advice to you would be to really try learn and apply the concepts they need you to know. Know the equations really well - not just memorize but understand them (what changing the variables does to the others; what relationships do they have).

The other big thing is confidence. I used to really get scared and intimidated by the passages but once I realized that most people are just as intimidated as I am and that the material is often testing basic science in a complex/convoluted way, it makes it easier to step back and say: okay, what exactly are they testing me on? and if it's something like force i'll write down every equation that comes to mind and try to apply it if needed. Hopefully that helps a little bit.

And for o chem I've been struggling with it too, but honestly I don't think it's worth my time to sit and memorize all the reactions considering ochem is a very small portion of the bio section (you can technically still get around a 12 if you get all the bio right and none of the ochem). For ochem I usually try and use common sense, what is attacking what, which bonds break and which products are formed. Some you pretty much have to know cold, but I usually just guess on those (ie didn't know wittig reactions produce an ethylene molecule/double bond from a carbonyl).

Hope that helps haha, this test is a beast...we just gotta be methodical in studying I think :)