Do you hear any noise as the antenna retracts?
Perhaps some "clicking" as the antenna stops retracting? I had the same problem on my '95, and was able to replace the antenna mast - for about $25. It's an easy fix if it is just the mast. That would be the place to start. You take off the nut on the antenna, turn on the radio which raises the antenna, grasp the antenna and pull it slightly as it raises, and it will come out. To install the new mast, you simply reverse this procedure, and it draws the mast back into the antenna motor, you put the nut back on, tighten it down, and it should (may) be fixed. Never fear, the replacement mast will come with instructions. BTW, I bought a GM mast.
However, I wound up having to remove my antenna motor, open it up and take out some mast that had broken off inside the housing. That took a couple of hours, but it was fun - if you like doing that sort of thing.
One other thing - don't push or pull on the antenna any more. You may get lucky and not have the plastic piece of the mast break off in the housing.
Good luck.