Why does my car says change oil when i just changed it

When this light illuminates, it means that the oil pressure in your vehicle's engine has dropped, and you need to take action immediately. If you continue to drive with this light on, you may cause serious damage to your vehicle's engine.

The oil-life minder must be reset after each oil change.

If your oil light comes on, you should try to have your vehicle inspected by a professional mechanic as soon as possible. Note, though, that driving around a bit more won't destroy anything. Generally speaking, you have about 2 weeks or 500 miles of driving before a flashing oil light turns into a legitimate problem.