I'm surprised you didn't get in your last two years... what part of your application was holding you back do you think?
I'll make it concise:
The first time was because I had limited clinical experience--I had shadowed two family physicians for a few hours each, and volunteered at a hospital for four months. I DID get two interviews (out of seven schools), and at one of them I was waitlisted.
I figured I'd have a pretty good shot if I applied the next year having been hired as an medical scribe in two ERs. However, the bar was set a lot higher the second time around, and although I had done another year of undergrad (after I graduated), did more tutoring, was a freshman RA, and then had the medical scribe job, it wasn't enough.
At the time, I had emailed the dean of admissions at which I was waitlisted, and he indicated i should get more clinical experience, maybe take a few more classes (if possible), and consider retaking my MCAT (at the time, the average matriculant scored a 33 at the school, and I had a 31). He recommended I take a year off, as applying immediately after the first cycle probably wouldn't be enough to get me over the hill.
Looking back, I THOUGHT I took him seriously, but he was absolutely right--applying in back-to-back cycles was a bad idea, and I really wasn't prepared my second time around. Thus, I was rejected by the school WITHOUT an interview the second time (same with the other school that interviewed me).
To summarize: it was a slight deficit that was exacerbated by me applying two straight years rather than taking a year off and making my application substantially stronger.