Sounds like siezed callipers, you have the symptoms. Check the temp of your alloys after driving. If noticibly hot, siezed calliper. Do you have a smell of burning when you get out of the car? What mechanic are you taking it to? I can't believe they'd keep changing discs and pads without noticing the calliper was seizing?? You'll keep going through lots of discs and pads if your callipers are seizing on!
Do a search, read some threads, lots of info on this. In my opinion most common fault on IS200! Had both my front callipers sieze 6 months apart.