2000 Oldsmobile Intrigue hard to turn streering wheel

Steering problem
2000 Oldsmobile Intrigue Front Wheel Drive Automatic 115000 miles

Hello,
I have recently purchased this vehicle used. I am finding a problem with the steering wheel especially when trying to park, or whenver you have to cut your wheels hard, the steering wheels becomes hard to turn, you have to struggle with iit, there is resistance, and sometimes a vibration to the steering wheel. To make an average turn it seems to be okay, just when there is a sharp cut, it is a problem. I am sure that the power steering fluid is full too. Do you know what is causing this? Jessica