Severe shaking in my Lebaron.

While driving down the road it starts shaking side to side and feels like you have a flat tire only worse (I've had a few to compare the feeling with!) The last time it continued for almost 10 miles and I coould only drive 30 miles an hour. It also makes a clunking sound when making a wide right turn. It doesn't do the shaking all the time but you never know when it is going to start. Any ideas?