Check the headphones you are using. Are they made for an iPod ? Or an iPhone? Some of the headphones made for phones can interfere with the buttons. The play/pause and volume buttons inline with the headphones are also used for answering the phone. Sometimes, the buttons can interfere with the proper operation of the iPod controls. If it is not the headphones, then there may be a physical problem with the iPod buttons. Do they feel normal? Is there sand or dust or water inside, possibly?