Transmission problem

I have a transmission that does not want to shift out of 2nd or 3rd gear.I can not tell which . I had the oil in it changed 3 weeks ago. It has been working fine until this . It is a 1998 Olds Cutless

The first thing you need to do is get the computer scanned for codes. Its possible that the transmission is in limp mode because the computer has detected a problem in the transmission or transmission controls. One of your local auto parts stores will probably scan the computer for free. Post back with the code/s. We need to know the code # and description.