I enrolled last July (2006), but didn't take my first exam until just this past May (2007). I didn't realize I could take exams before enrolling ... whoops. I was studying VERY slowly for A&P, but a couple of things helped me kick it up a notch -- first and foremost, I got a sizeable scholarship from the hospital's Ladies Board that I had to use within a year. The second thing was the discovery of study guides. Previously I had been working my way through the A&P textbook and the accompanying study guide. It was slow-going, but then I met another Paramedic who was doing the Excelsior thing, and he told me about the various YahooGroups for EC students. I joined a couple of those and read about TCN and Chancellor's study guides, and that's what I ended up using. So it really hasn't taken me all that long ... my first exam was May 14th, and my last concepts exam before I'll be CPNE-eligible is scheduled for 10/17. I still have to take Micro and do the sociology and human growth/development CLEPs in the interim, too.
Don't be hard on yourself for not taking exams yet ... but you're wise to set a deadline for yourself to get started.
Stick to it! My problem with A&P was that I never felt ready, never felt ready, never felt ready ... then I just went ahead and scheduled the darn thing! (And once I took one exam, I was just as you said you'd be -- full speed ahead!) I've done that for all my exams -- I schedule it, then study for it up to the deadline. It works well for me. You might find that some subjects will take you more than a month, some less, depending on your current level of knowledge of a particular subject.