That's kind of funny in a way... I'm just finishing up probably version 4 of a song that I started writing 3 years ago - I've never been happy with the bridge. I finally settled on A D A E A D A B
- talk about a boring progression - but it fit the melody so I'm going with it.
I wouldn't worry about how long it takes - it'll get faster as you go along. In the meantime, keep notes on the chord progressions that sound good to you. And if you can, look at the specific notes in each chord and see if you can see patterns regarding how one chord moves easily to another. Then experiment with other chords with similar note movements and see where that takes you.
That in a nutshell is how music theory was developed in the first place - and it changes all the time. Did you know Back was criticized for intoducing thirds into chords. Before him it was all power chords! Now we're coming back around...