So I broke a spoke a week ago, and when I put a new spoke in you know I trued it. Now, a week later, the bike feels like a kayak, because the back wheel is not very straight. Any idea why this would happen?

Some other information:

1. Hybrid road/mountain bike, single speed. Pretty tall, like a 62cm frame I think, with relatively small wheels.
2. I rode the bike with a broken spoke for another 30 miles or so before I had a chance to do something about it.
3. I wheel got so out of whack with my broken spoke that it caused trouble with the rear brake: if I jammed the rear brake, the brake pad would slip off the wheel.
4. Everything was fine up until the past few days

It's still rideable, and when I have a moment I'm going to go to the shop and true it again (hey, bikerowave!), but it seems like a waste of time to do that if there's some essential problem I'm ignoring.