Even if you had provided me with more information about your car I think I would still have a problem trying to answer this. The suspension of today's cars can be very complex. Meaning there are a lot of things that can go bad. All I can really tell you is to go and have a mechanic look at it.
There are many parts to a suspension. There is the rack and pinion, struts, inner tie rod, outer tie rod, ball joints and such. One have to diagnose and isolate the problem, then replace the faulty part.