Yeah I think everyone in this position can't help but think, why the hell am I doing this? and then just keep going, coz it's what you really want to do.
Personally, I've sometimes wondered if I'm crazy. I have a degree in business, so i could easily go get a boring office job, earn good money, buy an investment unit, get married and cheat on my wife. Instead, I'm trekking around Africa in search of that elusive 200hr flying job with a mountain of debt. But you know what? I'm glad I'm doing something exciting with my life and, eventually, when I'm sitting in the cockpit of the 747 as the sun rises, I will look fondly back at all of this and realize that it's worth it in the end (I like to think so anyway).
So just keep pluggin away (as I'm sure you're tired of hearing) and don't regret anything. I've met many people with regular jobs who wish they could be in my position.
Cheers