Complete focus when you're studying helps. Think about the material constantly. Find connections between all the material and think of them as one collective mass of information. Everything is related, think about how.
I think this is sound advice.
Also, what are you doing when you are studying?
My Ex-Gf and her sister both had this whacked out way of studying. They would just write everything down and highlight everything they thought was important... Well, if you're paying attention almost everything is important... The sister was the worst, her textbooks looked like someone spilled a confection of highlighters (4 colors), inks (prob 3 colors) and sticky tabs all over her textbooks... All her books should just be destroyed. Needless to say, she ALWAYS
felt prepared and would be lucky to scrape by in a class with a mid-range "B". She was wasting her time writing information she wasn't really paying attention to.
The key, at least in my opinion is like the above poster said, to focus on the material, visualize the systems, think them through (regardless of your class), and ask yourself conceptual questions about the material. If you can be honest with yourself and answer them then you're in business. If you just say, "yeah, yeah, I've got it. I understand" then you are going to be in trouble again.
Also, being able to just regurgitate facts isn't really learning the material. If you really understand the material you should be able to phrase it in a completely different way than it is phrased in your textbooks or was phrased by your prof (obviously equations are a little different, but you can still look at them from plenty of different angles). So, ask yourself thought questions like, what would happen if this mechanism were removed/inhibited/excited/competitively blocked, etc. Or what would happen if there was more of x than y (or less), or if you ever read a passage and say... Hmmm, I have no idea what that just meant, ask yourself what the author was supposed to be covering in the paragraph or group of paragraphs (it should be apparent by the heading/chapter), then reread it and try to pick out the key components that the author added to help make his point. Why did he use those terms here? How are they related to X topic? How is each term/concept related? How does this section fit in with the chapter content?
These are the best suggestions that I have for you. Sorry for being a little winded, but it really sounds like you're trying and haven't had any luck, so I hope some of the suggestions help.
If you continue to have problems after trying different things (oh, by the way, these types of study habits aren't formed overnight. They take a lot of practice, so give some of them and other suggestions a fair shake before you move on to the next), I would highly recommend you seek out a private tutor to study with you. This way he/she can ask you thought questions and you can try to answer them.
I wish you the best of luck, because I can't even imagine how frustrating this must be for you (although, I remember how frustrated the ex used to get).
). My tests are also multiple choice, but it's not hard at all. Before you even read the answers, you should try to answer it yourself. You said you were good at "filling in the blank" sort of questions, right? You "re-read and re-read", which isn't really ... well, I guess everyone has a different style, but when I read I try to summarize what they are saying in my own words (I write in my textbook). 
