gpg,
If you're having a hard time with biochem, well then just swicth to physio and stick with it. After you're done with physio, come back to biochem and things might be clearer then.
I know is supossed to be the other way around, but you never know sometimes. This certanly was the only way it worked for me.
I used a really tiny and thin book from the High Yield series. Is a USMLE part 1 Biochemestery review. It won't go into details, but it's really condensed and only tells you the main things into each cycle.
Biochem is like Russian or Japanese to me, a unknow unheard foreign language.