it feels excatly like i have a flat tire,but when i pull over and check all the on 2002 Buick Century

and appears no belt is broken

Asked by for the 2002 Buick Century
it may be a shifted belt in a tire. get it checked asap as it may fail completely.

1 more answer
When you jack the car up, you might as well pull on the tire top and bottom to make sure ball joints are ok too. Pull on tire at 9 and 3 o'clock positions to check tie rods as well. Can't hurt to do if you are raising the car to check tires out anyway.