2005 Toyota Echo Bumpy, wobbly ride

About a year and a half ago, I bought new tires for my Echo. After they were installed, I noticed that the car felt much bumpier and had a tendency to shift back and forth slightly, especially when driving on the freeway or on bumpy roads. I thought something was wrong with the tires, but the mechanics that installed them checked both them and the car itself and could find nothing wrong. Their reasoning was that the tires didn't offer as smooth as a ride as my old tires did, but I knew it was more than that.

Since then, I've had the tires replaced (having gone back to Goodyear, the same tires that were on it to begin with), and I've had the shocks and struts replaced, but the problem persists. Sometimes it's so bad that it makes my leg ache and go numb. Could they have somehow damaged the car in some way when replacing the tires the first time, or am I just going crazy? Could it be a problem with the springs (and are the springs separate from the struts and would therefore not have been replaced along with the struts)?