What is causing my car to wobble after hitting a bump?

[Smoked Neckbones]

I have a 94 lexus gs300. I had 3 alignments (within a month). After getting the first alignment I still had issues (Whenever I hit a bump especially on the highway my car bounces from side to side) It shifts from right to left then is fine til I hit another bump. I was told that it might be due to a bad upper control arm so I replaced both of them and I still have the same issue.

Initially I thought it was the tires since I went to one shop and said that since I didn't have matching tires that could be the reason. I went to another shop and they said the same thing. So after getting the tires I needed another alignment . This did not resolve the issue so I took it to another shop and they said it may be the Upper control arms